Author Topic: What is the cheapest and fastest way to go to the moon or mars  (Read 20607 times)

Offline Warren Platts

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IMO, the cheapest and fastest way to Mars would be a simple (as in pretty much fully propulsive), reusable (cheaper since it can be used over and over again), all chemical (faster than SEP), architecture that was evolved from previous spacecraft a la the ULA Lunar plan.

Zegler et al. say their DTAL lander could easily be evolved for use on Mars. My own BOTE calculations suggest that a stretched tank DTAL lander (i.e, an ACES-71) equipped with a heat resistant titanium hull (so it could withstand the full 1 W/cm2) could land fully propulsively--no ballutes, parachutes, or heat shields required.

Then the ULA MTV has a crew capacity of 16 and a nominal delta v of 11 km/sec. If there was refueling capability in Mars orbit, the ULA MTV could cut the 1-way transit times by over half compared to the Hohman transfer; if refueling was deemed impractical (probably the case for the initial missions), it would have enough delta v to do a round trip taking Hohman transfers. Again, this would all be fully propulsive--no heat shields required.

The 7 hundred tonnes of propellant would only cost about $350 million, if refueled at L2 (with Lunar derived LH2/LO2).

See, so the whole thing would be faster and cheaper, since it would be a simple evolution from the ULA Lunar architecture, which is itself a simple evolution from the Centaur 3rd-stage architecture.

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Offline DLR

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I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?

A Mars lander derived from ULA's DTAL would probably be equipped with a conical aeroshell and maybe a ballute, with propulsion being used for final deceleration and descent only. That way you save a lot of propellant as well.

Mars' atmosphere is a resource. Use it.
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Offline mmeijeri

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It is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.
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Offline Warren Platts

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I don't think we will use fully propulsive Mars landers. Ever tried firing a rocket into a hypersonic jet stream coming at you?

That's not the way it would work: the main burn happens in orbit above the atmosphere, and the lander essentially falls straight down, subsonically, until it achieves a terminal velocity, and then there's another burn right at landing.

Quote from: martijn
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Posted on: Today at 03:56 AMPosted by: mmeijeri 
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It is unlikely heavy payloads can be landed without using propulsion for substantially more than final descent and landing. Of course that doesn't mean you don't want to use aerodynamic deceleration to the maximum degree possible.

I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.
 
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Offline mmeijeri

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I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.

Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.
May Decatur do to SLS what Decatur did to the USS Philadelphia.

Offline Warren Platts

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I agree that other things being equal, you can save a lot of propellant by using aerobraking, but for heavy payloads, that's not trivial. There are faring issues as well. Meanwhile, a fully propulsive Mars lander could be had more or less off the shelf if it were a beefed up Lunar lander.

Hey, I'm all for that, in fact I've advocated just that. But eventually I think both propulsive braking and aerodynamic deceleration will play substantial roles. Large single-use heatshields that require huge fairings - not so much.

Roger that my friend! :)
"Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”--Leonardo Da Vinci

Offline spacenut

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Jim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.  There is also the possibility of an inflatable heat shield.  Mars' gravity and atmosphere is not as great as earth, like 35-40% I think. 

Offline Ben the Space Brit

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Mars' gravity and atmosphere is not as great as earth, like 35-40% I think. 

IIRC, Mars gravity is 0.28g and its atmosphere is 1mb, 1/1000 of Earth.

It is the latter that makes aerobraking a marginal (but not impossible) prospect and all-propulsive landing possible.
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Offline douglas100

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Surface gravity 38% Earth, average surface pressure around 7mb.
Douglas Clark

Offline spacenut

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So air braking might be just as costly as propulsive braking or landing? 

Offline 93143

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Jim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.

Only if it's a disk.  The DRM 5.0 aeroshells were biconics and 10 m across.

Online Robotbeat

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Jim has shown that a 10m heat shield can be folded in half to fit a 5m EELV.

Only if it's a disk.  The DRM 5.0 aeroshells were biconics and 10 m across.
And those aeroshells have never been tested on Mars. As long as we're doing that, why not a ballute?
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Offline mmeijeri

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So air braking might be just as costly as propulsive braking or landing? 

To answer that question you have to be very careful about which costs you include: development costs, fixed costs, variable costs? Another question is how this affects commercial launch prices. Once we have RLVs (or ISRU) propulsive solutions will become much more interesting. Conversely, starting with propulsive solutions can jump start development of RLVs through demand-pull or as Musk calls it, by providing a forcing function.
May Decatur do to SLS what Decatur did to the USS Philadelphia.

Offline Kaputnik

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IMO, the cheapest and fastest way to Mars would be a simple (as in pretty much fully propulsive), reusable (cheaper since it can be used over and over again), all chemical (faster than SEP), architecture that was evolved from previous spacecraft a la the ULA Lunar plan.

Zegler et al. say their DTAL lander could easily be evolved for use on Mars. My own BOTE calculations suggest that a stretched tank DTAL lander (i.e, an ACES-71) equipped with a heat resistant titanium hull (so it could withstand the full 1 W/cm2) could land fully propulsively--no ballutes, parachutes, or heat shields required.

Then the ULA MTV has a crew capacity of 16 and a nominal delta v of 11 km/sec. If there was refueling capability in Mars orbit, the ULA MTV could cut the 1-way transit times by over half compared to the Hohman transfer; if refueling was deemed impractical (probably the case for the initial missions), it would have enough delta v to do a round trip taking Hohman transfers. Again, this would all be fully propulsive--no heat shields required.

The 7 hundred tonnes of propellant would only cost about $350 million, if refueled at L2 (with Lunar derived LH2/LO2).

See, so the whole thing would be faster and cheaper, since it would be a simple evolution from the ULA Lunar architecture, which is itself a simple evolution from the Centaur 3rd-stage architecture.



Any links to the ULA Mars architecture?
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Offline Warren Platts

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http://www.ulalaunch.com/site/docs/publications/AffordableExplorationArchitecture2009.pdf

http://www.ulalaunch.com/site/docs/publications/DepotBasedTransportationArchitecture2010.pdf (this one has a cool picture of their proposed MTV)

http://www.ulalaunch.com/site/docs/publications/DualThrustAxisLander(DTAL)2009.pdf

These mostly describe ideas about how to do a Lunar program, but they say the Lunar architecture would be relatively easily evolved for use on Mars missions. It would be distinguishable from more conventional proposals in that the architecture would mostly  be reusable, and would probably take advantage of Lunar ISRU propellant (although they don't say this, Lunar propellant would be the only way to affordably fill up that MTV they propose).
"Once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return.”--Leonardo Da Vinci

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