Author Topic: Are Commercial Crew Vehicles Usable/Upgradeable for Beyond-LEO Needs?  (Read 46926 times)

Offline A_M_Swallow

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Dragon 2, from information I have found, has a dry mass of 6,350 kg and carries a total prop mass of 1815 kg including the abort propellant. 
At an ISP of 300s for the Draco thrusters that's 0.74 km/s bone dry no payload.  Well short of returning from anywhere other than L2.
Now adding a kick stage of sorts or trunk based propulsion is well within possibility, but not within the scope of the vehicle as designed.



And why not stage from L2? The gateway will be in a similar energy orbit.

Just because Apollo used LLO doesn't mean that we should or that it's ideal. Even Orion cannot use LLO unless it leaves LEO with a lander (or similar) attached, which tends to necessitate an expendable lander.

I think EML1,2, or a similar energy orbit would be more appropriate for staging as we already have multiple current or near-term vehicles that would be capable of reaching it with minimal modifications (Orion, Dragon, Starliner, Soyuz, possibly even Shenzhou, on top of SLS, Falcon Heavy, Vulcan Heavy or Vulcan with distributed lift, New Glenn, two launch Delta IV Heavy, Proton/Angara, Long March 5, etc).

As far as having enough room, Gemini was tiny and the two astronauts spent 2 weeks in LEO. 3 or so days transit (longer for a more efficient trajectory) is not a huge constraint. Dragon has much more room per crew than Gemini. Plenty for cislunar. Same with Starliner.

Also, LLO is terrible for staging anywhere but the Moon.

According to Wikipedia high thrust:
Delta-v LEO to L1 is 3.77 km/s
Delta-v L1 to LLO is 0.64 km/s
Delta-v LLO to Earth reentry is 1.31 km/s
Delta-v L1 to Moon surface is 2.52 km/s
Delta-v LLO to Moon surface is 1.87 km/s

If the Dragon 2 refuelled at a depot in L1 (or L2) it could fly to a spacestation in LLO. This is a good place to transfer to a lunar lander.

Cargo vehicles can move the propellant to the depot and spacestation without the high over head of having several tons of life support.

Offline yg1968

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And why not stage from L2? The gateway will be in a similar energy orbit.

Just because Apollo used LLO doesn't mean that we should or that it's ideal. Even Orion cannot use LLO unless it leaves LEO with a lander (or similar) attached, which tends to necessitate an expendable lander.

I think EML1,2, or a similar energy orbit would be more appropriate for staging as we already have multiple current or near-term vehicles that would be capable of reaching it with minimal modifications (Orion, Dragon, Starliner, Soyuz, possibly even Shenzhou, on top of SLS, Falcon Heavy, Vulcan Heavy or Vulcan with distributed lift, New Glenn, two launch Delta IV Heavy, Proton/Angara, Long March 5, etc).

As far as having enough room, Gemini was tiny and the two astronauts spent 2 weeks in LEO. 3 or so days transit (longer for a more efficient trajectory) is not a huge constraint. Dragon has much more room per crew than Gemini. Plenty for cislunar. Same with Starliner.

Also, LLO is terrible for staging anywhere but the Moon.

What about DC and Cygnus? Would they be able to make it to EML1,2 with minimal modifications?

Offline Robotbeat

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Cygnus, definitely. Dream chaser... I think so, with some work.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Coastal Ron

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As far as having enough room, Gemini was tiny and the two astronauts spent 2 weeks in LEO. 3 or so days transit (longer for a more efficient trajectory) is not a huge constraint. Dragon has much more room per crew than Gemini. Plenty for cislunar. Same with Starliner.

We were discussing the merits of LEO vehicles going beyond LEO on a different topic, and I don't disagree that it's possible for people to transport between LEO and the region of the Moon in Commercial Crew vehicles. If there are no other options, then I'm sure we can find some qualified people to go on those trips.

But the Gemini and Apollo flights were done by professionals that had trained for literally years for their flights. At some point going to space has to transition from "highly trained" to "lightly trained" individuals, otherwise cost will still be too high of a barrier to allow the private sector to help push humanity out into space - and I just don't see how we expand out into space without the private sector helping.

Based on that my view is that even if vehicles like Dragon Crew could be used for BLEO transportation, we shouldn't depend on them. Ignoring what SpaceX is doing, what everyone else should focus on is to build dedicated transportation segments that are serviced by vehicles designed for each segment.

For instance:

Earth-to-LEO = Commercial Crew vehicles and the like

LEO-to-Moon local = Reusable space-only vehicles, which obviously requires fuel depots and the ability to return to LEO (propulsively, use atmosphere to slow down, etc.)

Moon-local = Reusable landers

Beyond Earth Local Space = Reusable vehicles for expanding out beyond Earth local space, such as the Nautilus-X and NASA had suggested.

Now if the SpaceX ITS vehicles get perfected then maybe these plans change, but if the ITS do get perfected then we won't need Commercial Crew vehicles for leaving LEO anyways, so I'm not sure there's much merit in trying to modify Commercial Crew vehicles for going beyond LEO.

My $0.02
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Patchouli

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Cygnus, definitely. Dream chaser... I think so, with some work.

Cygnus is probably the easiest commercial vehicle to modify for BLEO use for various reasons including not needing to worry about beefing up the TPS.

Though I think DC does have more delta V than Dragon V2 or at least the crewed version did.
More room for propellant and less cosine losses.
« Last Edit: 08/01/2017 06:42 PM by Patchouli »

Offline envy887

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Cygnus, definitely. Dream chaser... I think so, with some work.

Cygnus is probably the easiest commercial vehicle to modify for BLEO use.

For cargo only and no Earth return, yes. Those are significant limitations for some applications.

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