United Launch Alliance has released some details on their concept for putting fuel depots into LEO to allow Moon-bound spacecraft to take aboard fuel on-orbit without having to carry it all the way to orbit with them: http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=spac... (when I saw that illustration, I thought they were proposing the old "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for a moment) ;-)
> United Launch Alliance has released some details on their concept for > putting fuel depots into LEO to allow Moon-bound spacecraft to take aboard > fuel on-orbit without having to carry it all the way to orbit with them: > http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=spac... > (when I saw that illustration, I thought they were proposing the old > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for a > moment) ;-)
I believe what the illustration shows is a "tanker" upper stage on the left and the LEO fuel depot on the right. The large fan like structure is a thermal shield to help keep the depot cold. The common cryogenic upper stage that they're developing seems like a logical starting point for a fuel depot.
Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
> United Launch Alliance has released some details on their concept for > putting fuel depots into LEO to allow Moon-bound spacecraft to take > aboard fuel on-orbit without having to carry it all the way to orbit > with them: > http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=space& > id=news/ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Station > s%20for%20Space%20Exploration (when I saw that illustration, I thought > they were proposing the old "PROFAC" nuclear ramjet LOX gatherer from > "The High Frontier" days for a moment) ;-)
Yeah, I thought so too, but it turns out just to be a sunshade for the propellant tanks.
In article <GvedneReQviV4R3XnZ2dnUVZ_hmdn...@posted.northdakotatelephone>, Pat Flannery <flan...@daktel.com> wrote:
> United Launch Alliance has released some details on their concept for > putting fuel depots into LEO to allow Moon-bound spacecraft to take > aboard fuel on-orbit without having to carry it all the way to orbit > with them: > http://www.aviationweek.com/aw/generic/story_channel.jsp?channel=spac... > /ULA08109.xml&headline=ULA%20Proposes%20On-Orbit%20Gas%20Stations%20for%20S pac > e%20Exploration > (when I saw that illustration, I thought they were proposing the old > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for a > moment) ;-)
> Pat
The idea sounds good -- at first. You can't just launch at any old time and expect to get there.
The problem is -- you have to get the launch and orbit planes lined up, reducing the launch window.
Next, you have to get the launch window correct for translunar flight.
Jeff Findley wrote: > I believe what the illustration shows is a "tanker" upper stage on the left > and the LEO fuel depot on the right. > The large fan like structure is a > thermal shield to help keep the depot cold.
I think that's the case also, but the illustration is fairly vague about what's going on. You can see that ULA is trying to figure out a way to get four guaranteed launches a year for Delta IV/Atlas V, so they can use those as a assured revenue stream, and make added profits off of any other launches they do. Unfortunately, if something like this is set up, it's going to be almost impossible to stop it at some future point from a political point of view, as ULA will be counting on the four launches even after any Moon exploration ends. So then they will start lobbying for a new program to use this "valuable national space resource" on. You can see that one coming a mile off. :-)
Orval Fairbairn wrote: > The idea sounds good -- at first. You can't just launch at any old time > and expect to get there.
> The problem is -- you have to get the launch and orbit planes lined up, > reducing the launch window.
Well, at least the booster should have more lax weather constraints than the Shuttle, and that should help with getting into the launch window. If we ever were going to get into the Moon game big time, it would be wise to consider building a new launch facility somewhere a lot closer to the equator, and where the summer weather is better than at the Cape.
> Next, you have to get the launch window correct for translunar flight.
What are the launch windows for a Moon flight like from the equator versus the Cape? Can you launch more often from down there? You would get significantly more payload into LEO with a equatorial launch.
> Jeff Findley wrote: >> I believe what the illustration shows is a "tanker" upper stage on the >> left and the LEO fuel depot on the right. >> The large fan like structure is a thermal shield to help keep the depot >> cold.
> I think that's the case also, but the illustration is fairly vague about > what's going on. > You can see that ULA is trying to figure out a way to get four guaranteed > launches a year for Delta IV/Atlas V, so they can use those as a assured > revenue stream, and make added profits off of any other launches they do. > Unfortunately, if something like this is set up, it's going to be almost > impossible to stop it at some future point from a political point of view, > as ULA will be counting on the four launches even after any Moon > exploration ends. > So then they will start lobbying for a new program to use this "valuable > national space resource" on. > You can see that one coming a mile off. :-)
Depends if NASA is smart enough to separate the depot bid from the ongoing tanker bids (I would hope they are). The way you do this is make sure that the RFP for the depot is written in such a way as to force the docking and propellant transfer interfaces to be made public. That way ULA will need to compete for tanker bids on a level playing field with other, potentially cheaper, launch providers.
Also, as I've said in the past, the tankers could even be paid for and flown by other nations in exchange for seats on "international" Orion missions.
Jeff -- "Take heart amid the deepening gloom that your dog is finally getting enough cheese" - Deteriorata - National Lampoon
> Depends if NASA is smart enough to separate the depot bid from the ongoing > tanker bids (I would hope they are). The way you do this is make sure that > the RFP for the depot is written in such a way as to force the docking and > propellant transfer interfaces to be made public. That way ULA will need to > compete for tanker bids on a level playing field with other, potentially > cheaper, launch providers.
> Also, as I've said in the past, the tankers could even be paid for and flown > by other nations in exchange for seats on "international" Orion missions.
> Jeff
That will work fine till the Russian space tanker rams the US fuel depot while trying to dock, and all hell breaks loose internationally.
> Orval Fairbairn wrote: > > The idea sounds good -- at first. You can't just launch at any old time > > and expect to get there.
> > The problem is -- you have to get the launch and orbit planes lined up, > > reducing the launch window.
> Well, at least the booster should have more lax weather constraints than > the Shuttle, and that should help with getting into the launch window. > If we ever were going to get into the Moon game big time, it would be > wise to consider building a new launch facility somewhere a lot closer > to the equator, and where the summer weather is better than at the Cape.
> > Next, you have to get the launch window correct for translunar flight.
> What are the launch windows for a Moon flight like from the equator > versus the Cape? Can you launch more often from down there? You would > get significantly more payload into LEO with a equatorial launch.
No real difference there -- the Moon, IIRC, has a 23.5 deg inclination to the equator, very close to that of the Ecliptic. Of course, you CAN approach the Moon at numerous inclinations, but the Earth-Moon transfer still has to be in the neighborhood of 23.5 deg.
Orval Fairbairn wrote: > In article > <id2dnU3syoO7NhzXnZ2dnUVZ_gSdn...@posted.northdakotatelephone>, > Pat Flannery <flan...@daktel.com> wrote:
>> Orval Fairbairn wrote: >>> The idea sounds good -- at first. You can't just launch at any old time >>> and expect to get there.
>>> The problem is -- you have to get the launch and orbit planes lined up, >>> reducing the launch window.
>> Well, at least the booster should have more lax weather constraints than >> the Shuttle, and that should help with getting into the launch window. >> If we ever were going to get into the Moon game big time, it would be >> wise to consider building a new launch facility somewhere a lot closer >> to the equator, and where the summer weather is better than at the Cape.
>>> Next, you have to get the launch window correct for translunar flight.
>> What are the launch windows for a Moon flight like from the equator >> versus the Cape? Can you launch more often from down there? You would >> get significantly more payload into LEO with a equatorial launch.
> No real difference there -- the Moon, IIRC, has a 23.5 deg inclination > to the equator, very close to that of the Ecliptic. Of course, you CAN > approach the Moon at numerous inclinations, but the Earth-Moon transfer > still has to be in the neighborhood of 23.5 deg.
Consider that the moon crosses the equatorial plane every 14 days, and aim for that point from equatorial LEO, with no plane changes necessary (and using the same total delta-V as an inclined plane orbit with a stop in LEO).
There isn't much to be gained, as far as lunar operations go, in using an inclined orbit. A minimum-fuel launch window every 14 days is enough.
The best place for a fuel depot / station is in equatorial orbit because:
1) you get the most benefit from the Earth's rotation, and thus the highest payload.
2) you can launch to it from any point on the Earth's equator every 90 minutes.
3) you can do first orbit rendezvous every 90 minutes.
This means that the flight time is a minimum, and for instance eg passengers don't need meals, toilets, beds etc (half a Soyuz is taken up by that stuff, as it takes them several days to rendezvous with the Space Station: for a passenger flight this *doubles* capacity, or more), with frequent flights urgent supplies can arrive in a couple of hours from when they arrive at the launch site, and any reuseable cargo hardware is back on the ground quicker, increasing turnaround.
4) you can minimum-fuel transfer to anywhere in GSO every 90 minutes,
5) you have a minimum-fuel lunar launch window every 14 days.
The main disadvantage is the scenery isn't very pretty, it's mostly ocean with occasional desert or jungle. Few Tourists will be able to say "I can see my home from here".
The other disadvantage is that you need to launch from somewhere on the equator, but that's just politics mostly.
You need a tug in orbit though, preferably manned - supplies etc should be delivered to near the station, and final placement/docking is done by the tug. This means the station/tug is mainly responsible for safety, which is sensible as it's their safety.
> Orval Fairbairn wrote: > > In article > > <id2dnU3syoO7NhzXnZ2dnUVZ_gSdn...@posted.northdakotatelephone>, > > Pat Flannery <flan...@daktel.com> wrote:
> >> Orval Fairbairn wrote: > >>> The idea sounds good -- at first. You can't just launch at any old time > >>> and expect to get there.
> >>> The problem is -- you have to get the launch and orbit planes lined up, > >>> reducing the launch window.
> >> Well, at least the booster should have more lax weather constraints than > >> the Shuttle, and that should help with getting into the launch window. > >> If we ever were going to get into the Moon game big time, it would be > >> wise to consider building a new launch facility somewhere a lot closer > >> to the equator, and where the summer weather is better than at the Cape.
> >>> Next, you have to get the launch window correct for translunar flight.
> >> What are the launch windows for a Moon flight like from the equator > >> versus the Cape? Can you launch more often from down there? You would > >> get significantly more payload into LEO with a equatorial launch.
> > No real difference there -- the Moon, IIRC, has a 23.5 deg inclination > > to the equator, very close to that of the Ecliptic. Of course, you CAN > > approach the Moon at numerous inclinations, but the Earth-Moon transfer > > still has to be in the neighborhood of 23.5 deg.
> Consider that the moon crosses the equatorial plane every 14 days, and > aim for that point from equatorial LEO, with no plane changes necessary > (and using the same total delta-V as an inclined plane orbit with a stop > in LEO).
> There isn't much to be gained, as far as lunar operations go, in using > an inclined orbit. A minimum-fuel launch window every 14 days is enough.
> The best place for a fuel depot / station is in equatorial orbit because:
> 1) you get the most benefit from the Earth's rotation, and thus the > highest payload.
> 2) you can launch to it from any point on the Earth's equator every 90 > minutes.
> 3) you can do first orbit rendezvous every 90 minutes.
> This means that the flight time is a minimum, and for instance eg > passengers don't need meals, toilets, beds etc (half a Soyuz is taken up > by that stuff, as it takes them several days to rendezvous with the > Space Station: for a passenger flight this *doubles* capacity, or more), > with frequent flights urgent supplies can arrive in a couple of hours > from when they arrive at the launch site, and any reuseable cargo > hardware is back on the ground quicker, increasing turnaround.
> 4) you can minimum-fuel transfer to anywhere in GSO every 90 minutes,
> 5) you have a minimum-fuel lunar launch window every 14 days.
> The main disadvantage is the scenery isn't very pretty, it's mostly > ocean with occasional desert or jungle. Few Tourists will be able to say > "I can see my home from here".
> The other disadvantage is that you need to launch from somewhere on the > equator, but that's just politics mostly.
> You need a tug in orbit though, preferably manned - supplies etc should > be delivered to near the station, and final placement/docking is done by > the tug. This means the station/tug is mainly responsible for safety, > which is sensible as it's their safety.
> Orval Fairbairn wrote: > > In article > > <id2dnU3syoO7NhzXnZ2dnUVZ_gSdn...@posted.northdakotatelephone>, > > Pat Flannery <flan...@daktel.com> wrote:
> >> Orval Fairbairn wrote: > >>> The idea sounds good -- at first. You can't just launch at any old ti me > >>> and expect to get there.
> >>> The problem is -- you have to get the launch and orbit planes lined u p, > >>> reducing the launch window.
> >> Well, at least the booster should have more lax weather constraints th an > >> the Shuttle, and that should help with getting into the launch window. > >> If we ever were going to get into the Moon game big time, it would be > >> wise to consider building a new launch facility somewhere a lot closer > >> to the equator, and where the summer weather is better than at the Cap e.
> >>> Next, you have to get the launch window correct for translunar flight .
> >> What are the launch windows for a Moon flight like from the equator > >> versus the Cape? Can you launch more often from down there? You would > >> get significantly more payload into LEO with a equatorial launch.
> >> Pat
> >> MODERATOR'S COMMENT: > >> JDL
> > No real difference there -- the Moon, IIRC, has a 23.5 deg inclination > > to the equator, very close to that of the Ecliptic. Of course, you CAN > > approach the Moon at numerous inclinations, but the Earth-Moon transfer > > still has to be in the neighborhood of 23.5 deg.
> Consider that the moon crosses the equatorial plane every 14 days, and > aim for that point from equatorial LEO, with no plane changes necessary > (and using the same total delta-V as an inclined plane orbit with a stop > in LEO).
> There isn't much to be gained, as far as lunar operations go, in using > an inclined orbit. A minimum-fuel launch window every 14 days is enough.
> The best place for a fuel depot / station is in equatorial orbit because:
> 1) you get the most benefit from the Earth's rotation, and thus the > highest payload.
> 2) you can launch to it from any point on the Earth's equator every 90 > minutes.
> 3) you can do first orbit rendezvous every 90 minutes.
> This means that the flight time is a minimum, and for instance eg > passengers don't need meals, toilets, beds etc (half a Soyuz is taken up > by that stuff, as it takes them several days to rendezvous with the > Space Station: for a passenger flight this *doubles* capacity, or more), > with frequent flights urgent supplies can arrive in a couple of hours > from when they arrive at the launch site, and any reuseable cargo > hardware is back on the ground quicker, increasing turnaround.
> 4) you can minimum-fuel transfer to anywhere in GSO every 90 minutes,
> 5) you have a minimum-fuel lunar launch window every 14 days.
> The main disadvantage is the scenery isn't very pretty, it's mostly > ocean with occasional desert or jungle. Few Tourists will be able to say > "I can see my home from here".
> The other disadvantage is that you need to launch from somewhere on the > equator, but that's just politics mostly.
> You need a tug in orbit though, preferably manned - supplies etc should > be delivered to near the station, and final placement/docking is done by > the tug. This means the station/tug is mainly responsible for safety, > which is sensible as it's their safety.
> -- Peter Fairbrother
> MODERATOR'S COMMENT: > JDL
There's nothing better than using the to/from delta-V of our Selene L1.
~ BG
MODERATOR'S COMMENT: Please consider trimming your quotes in the future. JDL
> > United Launch Alliance has released some details on their concept for > > putting fuel depots into LEO to allow Moon-bound spacecraft to take abo ard > > fuel on-orbit without having to carry it all the way to orbit with them : > >http://www.aviationweek.com/aw/generic/story_channel.jsp?channelspac. .. > > (when I saw that illustration, I thought they were proposing the old > > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for a > > moment) ;-)
> I believe what the illustration shows is a "tanker" upper stage on the le ft > and the LEO fuel depot on the right. The large fan like structure is a > thermal shield to help keep the depot cold. The common cryogenic upper > stage that they're developing seems like a logical starting point for a f uel > depot.
> Jeff > -- > "Take heart amid the deepening gloom > that your dog is finally getting enough cheese" - Deteriorata - National > Lampoon
> .
If using h2o2 + synfuel, there's hardly any thermal issues or subsequent loss of fuel tonnage.
Orval Fairbairn wrote: > In article > <id2dnU3syoO7NhzXnZ2dnUVZ_gSdn...@posted.northdakotatelephone>, > Pat Flannery <flan...@daktel.com> wrote:
>> Orval Fairbairn wrote: >>> The idea sounds good -- at first. You can't just launch at any old time >>> and expect to get there.
>>> The problem is -- you have to get the launch and orbit planes lined up, >>> reducing the launch window.
>> Well, at least the booster should have more lax weather constraints than >> the Shuttle, and that should help with getting into the launch window. >> If we ever were going to get into the Moon game big time, it would be >> wise to consider building a new launch facility somewhere a lot closer >> to the equator, and where the summer weather is better than at the Cape.
>>> Next, you have to get the launch window correct for translunar flight.
>> What are the launch windows for a Moon flight like from the equator >> versus the Cape? Can you launch more often from down there? You would >> get significantly more payload into LEO with a equatorial launch.
> No real difference there -- the Moon, IIRC, has a 23.5 deg inclination > to the equator, very close to that of the Ecliptic. Of course, you CAN > approach the Moon at numerous inclinations, but the Earth-Moon transfer > still has to be in the neighborhood of 23.5 deg.
Expanding on that a bit:
The Moon's orbit has a 5.5 degree inclination with respect to the ecliptic. The inclination with respect to the equator depends on the orientation of the Moon's line of nodes, which regresses around its orbit with a period of 18.5 years, varying between a minimum of 18 degrees and a maximum of 29 degrees.
In 1969, the Moon's ascending node happened to be close to the vernal equinox, resulting in an inclination near the maximum, and coincidentally close to the latitude of KSC.
The TLI burn must be performed at or near the Moon's antipode, the projection of the Earth-Moon vector through the Earth's center to the opposite side. So the LEO parking orbit plane must pass through the antipode. That implies the launch inclination must be greater than the declination of the moon, otherwise the antipode will not intersect the orbital plane.
Since Apollo could launch a lunar mission with a single Saturn V, they could meet this requirement and still have a relatively wide launch window by the use of variable-azimuth launch targeting. The azimuth limits were typically 72-108 degrees, or 18 degrees north or south of due east. This resulted in orbit inclinations between 28.5 and 33.3 degrees, and a daily launch window of around 2.5 hours.
Not so with an EOR architecture. You can use variable azimuth targeting on the first element, but after that the launch times of the subsequent elements are fixed entirely by the planar/phase requirements for rendezvous with the previous elements, and TLI opportunities are similarly fixed. Equatorial orbits do not necessarily provide an advantage here; they provide more frequent (and longer) launch windows for the subsequent elements, but TLI opportunities are limited to when the antipode crosses the equator, which only happens twice per month and will only rarely coincide with desired lighting conditions at the landing site.
> > > United Launch Alliance has released some details on their concept for > > > putting fuel depots into LEO to allow Moon-bound spacecraft to take abo > ard > > > fuel on-orbit without having to carry it all the way to orbit with them > : > > >http://www.aviationweek.com/aw/generic/story_channel.jsp?channelÙac. > .. > > > (when I saw that illustration, I thought they were proposing the old > > > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for > a > > > moment) ;-)
> > I believe what the illustration shows is a "tanker" upper stage on the le > ft > > and the LEO fuel depot on the right. The large fan like structure is a > > thermal shield to help keep the depot cold. The common cryogenic upper > > stage that they're developing seems like a logical starting point for a f > uel > > depot.
> > Jeff > > -- > > "Take heart amid the deepening gloom > > that your dog is finally getting enough cheese" - Deteriorata - National > > Lampoon
> > .
> If using h2o2 + synfuel, there's hardly any thermal issues or > subsequent loss of fuel tonnage.
> ~ BG
Yes -- but you sacrifice payload for a low performance propellant combination. Remember -- you get only one oxygen atom from a molecule of H2O2.
> > > > United Launch Alliance has released some details on their concept f or > > > > putting fuel depots into LEO to allow Moon-bound spacecraft to take abo > > ard > > > > fuel on-orbit without having to carry it all the way to orbit with them > > : > > > >http://www.aviationweek.com/aw/generic/story_channel.jsp?channelÙa c. > > .. > > > > (when I saw that illustration, I thought they were proposing the ol d > > > > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for > > a > > > > moment) ;-)
> > > I believe what the illustration shows is a "tanker" upper stage on th e le > > ft > > > and the LEO fuel depot on the right. The large fan like structure is a > > > thermal shield to help keep the depot cold. The common cryogenic u pper > > > stage that they're developing seems like a logical starting point for a f > > uel > > > depot.
> > > Jeff > > > -- > > > "Take heart amid the deepening gloom > > > that your dog is finally getting enough cheese" - Deteriorata - Natio nal > > > Lampoon
> > > .
> > If using h2o2 + synfuel, there's hardly any thermal issues or > > subsequent loss of fuel tonnage.
> > ~ BG
> Yes -- but you sacrifice payload for a low performance propellant > combination. Remember -- you get only one oxygen atom from a molecule of > H2O2.
H2O2 + synfuel maximum energy density and thus terrific energy value, not to mention near zero storage loss has got to be worth something.
~ BG
MODERATOR'S COMMENT: Have a link to a description of the synfuel anywhere? JDL
> > > > United Launch Alliance has released some details on their concept f or > > > > putting fuel depots into LEO to allow Moon-bound spacecraft to take abo > > ard > > > > fuel on-orbit without having to carry it all the way to orbit with them > > : > > > >http://www.aviationweek.com/aw/generic/story_channel.jsp?channelÙa c. > > .. > > > > (when I saw that illustration, I thought they were proposing the ol d > > > > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for > > a > > > > moment) ;-)
> > > I believe what the illustration shows is a "tanker" upper stage on th e le > > ft > > > and the LEO fuel depot on the right. The large fan like structure is a > > > thermal shield to help keep the depot cold. The common cryogenic u pper > > > stage that they're developing seems like a logical starting point for a f > > uel > > > depot.
> > > Jeff > > > -- > > > "Take heart amid the deepening gloom > > > that your dog is finally getting enough cheese" - Deteriorata - Natio nal > > > Lampoon
> > > .
> > If using h2o2 + synfuel, there's hardly any thermal issues or > > subsequent loss of fuel tonnage.
> > ~ BG
> Yes -- but you sacrifice payload for a low performance propellant > combination. Remember -- you get only one oxygen atom from a molecule of > H2O2.
> -- > Remove _'s from email address to talk to me.
On Aug 10, 1:00 pm, Pat Flannery <flan...@daktel.com> wrote:
> United Launch Alliance has released some details on their concept for > putting fuel depots into LEO to allow Moon-bound spacecraft to take > aboard fuel on-orbit without having to carry it all the way to orbit > with them:http://www.aviationweek.com/aw/generic/story_channel.jsp?channe lspac... > (when I saw that illustration, I thought they were proposing the old > "PROFAC" nuclear ramjet LOX gatherer from "The High Frontier" days for a > moment) ;-)
> Pat
----- It would seem simpler to launch pre-filled tanks and mate the tanks with contents in orbit. Pumping from a fueling station seems just added steps and hardware.
Anvil* wrote: > It would seem simpler to launch pre-filled tanks and mate the tanks > with contents > in orbit. Pumping from a fueling station seems just added steps and > hardware.
The big problem is the added weight and complexity (not to mention cost) of putting the rendezvous, docking gear, and RCS on the tanker so that it can transfer its propellants to the orbiting depot. From a weight and cost viewpoint, it might make more sense to have the depot be able to go to and dock with the tanker once it gets into orbit as the _active_ partner in the docking, rather than the other way around. The more aspects of the docking equipment you put aboard the depot, the less you lose when the tanker burns up on reentry.
Pat Flannery wrote: > Anvil* wrote: >> It would seem simpler to launch pre-filled tanks and mate the tanks >> with contents >> in orbit. Pumping from a fueling station seems just added steps and >> hardware.
Yes, in almost all cases, though you might occasionally want to split a tankload if you have spare tanks available, eg from a lunar or LEO-GSO shuttle.
> The big problem is the added weight and complexity (not to mention cost) > of putting the rendezvous, docking gear, and RCS on the tanker so that > it can transfer its propellants to the orbiting depot. > From a weight and cost viewpoint, it might make more sense to have the > depot be able to go to and dock with the tanker once it gets into orbit > as the _active_ partner in the docking, rather than the other way around. > The more aspects of the docking equipment you put aboard the depot, the > less you lose when the tanker burns up on reentry.
> Pat
A tug is even better (after only about 4 fuel launches, depending on details), as that way you don't have to move all the mass of the depot, just the mass of the tug plus the new fuel tank.
A tug has several other advantages, eg the rendezvous doesn't have to be as accurate, and it keeps the tanks apart from the depot until the depot is ready to receive them - if you like you can also keep the fuel tanks far from the depot, on maybe a tether or a long boom, and just move them to where they are needed, maybe joining them to the ongoing spacecraft at a point far enough from the depot to prevent a catastrophic tank failure from destroying the depot.
You can also keep fuel and oxidiser tanks far apart from each other, which minimises the danger of accidental mixing, eg after meteorite impact.
Initially of course a depot can just be a location in orbit with no hardware there at all - send up a few tanks, and then get the onward-going space craft to collect them.
Another advantage of a (slightly more advanced) orbital depot is that is actually makes cheap access to space easier. Each launcher can be smaller than the big ones (I reckon the sweet spot is about 8 tons equatorial LEO payload). For a smaller launcher you don't need as many billions upfront, or as expensive assembly buildings, launch pads and GSE.
So what form should this launch system take?
For lots of reasons, a two-version TSTO with a common highly-reuseable fuel-and-go-again winged flyback first stage, and two versions of the second stage, one reentering version for people and one partly expendable (just bring back the expensive bits like engines and electronics) version for cargo, is by far the best.
For a LOX/kero first stage and a LOX/LH2 second stage, with an 8 ton payload, TOW is about 450 tons, about the same as a 747 or big Airbus, which means a good runway can be used for HTHL takeoff and landing, or if you want VTHL you can land on a much smaller runway, as the landing weight is only about 120 tons - however that means having a dedicated launchpad, rather than just propellent supplies and a hanger at a runway, so I'd suggest HTHL is the way to go - it's also slightly cheaper in fuel terms.
Peter Fairbrother <zenadsl6...@zen.co.uk> wrote: >Another advantage of a (slightly more advanced) orbital depot is that is >actually makes cheap access to space easier.
It makes cheap *launchers* possible - at the cost of making the system as a whole more expensive and complicated.
> Another advantage of a (slightly more advanced) orbital depot is that is > actually makes cheap access to space easier. Each launcher can be > smaller than the big ones (I reckon the sweet spot is about 8 tons > equatorial LEO payload). For a smaller launcher you don't need as many > billions upfront, or as expensive assembly buildings, launch pads and GSE.
> So what form should this launch system take?
> For lots of reasons, a two-version TSTO with a common highly-reuseable > fuel-and-go-again winged flyback first stage, and two versions of the > second stage, one reentering version for people and one partly > expendable (just bring back the expensive bits like engines and > electronics) version for cargo, is by far the best.
> For a LOX/kero first stage and a LOX/LH2 second stage, with an 8 ton > payload, TOW is about 450 tons, about the same as a 747 or big Airbus, > which means a good runway can be used for HTHL takeoff and landing, or > if you want VTHL you can land on a much smaller runway, as the landing > weight is only about 120 tons - however that means having a dedicated > launchpad, rather than just propellent supplies and a hanger at a > runway, so I'd suggest HTHL is the way to go - it's also slightly > cheaper in fuel terms.
> About $7-8 billion in development costs.
The problem with all this infrastructure and its cost is that unless you are intending to make frequent trips to and beyond LEO over a period of many years, you can't justify the long range cost savings of developing it. With a high enough launch rate the Shuttle would have been cheaper than expendable rockets; unfortunately that was when the yearly launch rate went into the hundreds, which wasn't going to happen in any foreseeable future for the simple reason that there weren't that many combined science, commercial, and military payloads that needed to be launched in any given year.
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