Could SLS work for a Mars Direct architecture?

[redliox]

Until a company like Blue Origin or SpaceX finally assemble their heavy lift vehicles, the current best option for a HLV is the SLS which is nearing completion.  Space policy aside, either the SLS 1B or 2 versions could be of great use to a Mars program.  In this case, I'm looking at the Mars Direct or Semi-Direct schemes and posing the question:

Could the SLS work for Mars Direct?

Eventually, the SLS could be phased out for a cheaper vehicle, but the future is foggy in light of the incoming administration.  However I'm not so much talking about space policy but rather whether the SLS could serve the role of the "Ares" in Zubrin's schemes.  If not I'm curious to know what is lacking, or if delivering payloads ahead to Mars could compensate while retaining a 2-3 launch scheme.

[RonM]

Well, SLS is basically what Zubrin was talking about, shuttle derived rocket tossing about 40 tonnes towards Mars.

What is lacking is money and time to develop the payloads before SpaceX has their ITS system ready. Current thought based on budget reality is to start having Mars missions in the 2030s through 2040s. If SpaceX can get their act together they will beat NASA to Mars. Then again, SpaceX might not be able to pull off the funding for ITS, so NASA may still get to use SLS for Mars.

Who knows what the new administration will do. They might continue funding SLS, pay SpaceX, or forget about Mars altogether.

[redliox]

Well, SLS is basically what Zubrin was talking about, shuttle derived rocket tossing about 40 tonnes towards Mars.

The masses advocated for a 1B or 2 seemed in the range Zubrin wanted, and obviously SpaceX has taken this deep to heart in the ITS plans and then-some.

What is lacking is money and time to develop the payloads before SpaceX has their ITS system ready. Current thought based on budget reality is to start having Mars missions in the 2030s through 2040s. If SpaceX can get their act together they will beat NASA to Mars. Then again, SpaceX might not be able to pull off the funding for ITS, so NASA may still get to use SLS for Mars.

Who knows what the new administration will do. They might continue funding SLS, pay SpaceX, or forget about Mars altogether.

Politics is an irritating wild card.  It's pretty much responsible for the 1980s and 90s being largely vacant of human or robotic missions with value, up until Sojourner rolled onto Mars near the end.  Like many I do hope to see SpaceX succeed but I suspect we may have to settle for something like SLS complemented by Falcon Heavys...under ideal current circumstances.

[MATTBLAK]

With the most feasible version of SLS that could come to pass - a Block 2 or '2b' - the traditional Mars Direct vehicles could just squeak into the SLS TMI payload figures - without getting too much into 'Rocket Lego' wishlist modifications to SLS. Make sure to tap Steve Pietrobon for his previous SLS calculations:

4x RS-25E engine corestage, 2x 5-Segment SRBs, 4x RL-10 powered Exploration Upper Stage (EUS): 39 or 40 tons direct to Trans-Mars Injection. Refer to Zubrin & Baker's documentation for M.D. vehicle mass breakdown.

SLS Feasibly & sensibly uprated: 2x 'Dark Knights' SRBs, EUS powered by higher thrust replacements for the RL-10; such as the MB-60 or Vinci engines. RS-25E uprated for higher thrust. All that would probably only boost the TMI payload to 45-47 tons - about the same as the Saturn V. Still impressive, though.

For vehicles of roughly similar capability to this - look to Blue Origin's 'New Glenn' boosters and their successors. I'd like to see Zubrin re-crunch the numbers to use a mixed-twin launch fleet of Falcon Heavy with an uprated upper stage and the most capable version of Vulcan/ACES! If Zubrin resized the Mars Direct vehicles for a crew of 3 or even only 2 Astronauts; Vulcan could launch the spacecraft and Falcon Heavy could follow the next day with an Earth Departure stage for it to rendezvous and dock with. That EDS stage could contain about 55 tons of propellants - whether that be LOX/Kerosene or LOX/CH4 - assuming the Falcon Heavy upper stage had been uprated to using a single vacuum-optimized Raptor engine. The Mars Direct vehicle could use it's own propulsion system to augment the EDS burn. Or maybe Zubrin could think outside the box and include a couple Hall thrusters and some Xenon propellant on the Mars vehicle to use as a 'cruise engine' to shape the trajectory over several days.

[AncientU]

The OP discussed SLS as 'nearing' completion* -- proposed concepts are a dozen years in the future or not even on the drawing boards.

* Nearing is used loosely in the OP.  Crew flight is still approximately as distant into the future as when the program was begun in 2010-11.

[Oli]

Mars Direct falls apart once you consider a realistically sized return payload.

But regardless, any "direct" architecture is suboptimal because all launches must be concentrated within one month or so every 2 years.

For a good use of SLS I would suggest making EUS refuelable.

[MATTBLAK]

Refueling of multi-hundred tons cryogenics in space has never been done. But get on to that asap, I say!

[Darkseraph]

Block 2 SLS would more or less work for Mars Direct. It has similar performance to the proposed Ares. For various reasons I don't know the details of, NASA has moved far away from such a lean mission architecture. Most of their proposed Mars missions are now hundreds of tons IMLEO split over half a dozen or more launches of Block 2 SLS.

[redliox]

The OP discussed SLS as 'nearing' completion* -- proposed concepts are a dozen years in the future or not even on the drawing boards.

* Nearing is used loosely in the OP.  Crew flight is still approximately as distant into the future as when the program was begun in 2010-11.

Nearing isn't that loosely used.  Payloads for SLS are years into the future, but the boosters and core are being physically built and tested which is a huge step away from mere paperwork.  Also, unlike the Ares I-X test, most elements of the Block I version for the 2018 EM-1 flight are going to be identical for the IB version.  Only the upper stage, EUS, needs to be built to transition from I to IB.  The SLS is literally being made real regardless of opinion and administrations.

Unlike either Glen or ITS, the SLS isn't purely blueprints or proposal porn anymore.  It is, momentarily, THE heavy launch vehicle.  With luck, the Falcon Heavy will join this roster but more like a HLV "lite."  SLS is going to fly before any other HLV of similar or better capability.

Mars Direct falls apart once you consider a realistically sized return payload.

Not as quickly as the 1980s SEI, the 2000s Vision, or ARM.  However, any plan can be improved or modified.  Part of the process involves looking at what's currently available, and only SLS and FH will be available before 2020.

Block 2 SLS would more or less work for Mars Direct. It has similar performance to the proposed Ares. For various reasons I don't know the details of, NASA has moved far away from such a lean mission architecture. Most of their proposed Mars missions are now hundreds of tons IMLEO split over half a dozen or more launches of Block 2 SLS.

Sadly that's exactly the same as for SEI, and that fell flat on its face once Congress saw the price tag.  NASA will either have to lean down or (more likely) SpaceX will indeed "win the race."

[Hanelyp]

How few launches over how many years, and how far in the future, are they looking at for SLS these days?

[Oli]

Not as quickly as the 1980s SEI, the 2000s Vision, or ARM.

Not sure what you mean.

However, any plan can be improved or modified. 

Yes, SpaceX has the Mars Direct (return) plan that works.

Refueling of multi-hundred tons cryogenics in space has never been done. But get on to that asap, I say!

The alternative is SEP, which is nice but a unique capability when sized for human spaceflight applications. That means a lack of competition and potentially high cost.

The other alternative is something like JPL's plan or the DRMs but they rely on SLS only.

I think bringing commercial space as well as international participation into a Mars program is crucial. EUS could be a nice departure stage, if sized properly, and refueling it would give plenty of work to commercial/internationals.

[Endeavour_01]

Could the SLS work for Mars Direct?

Well, SLS is basically what Zubrin was talking about, shuttle derived rocket tossing about 40 tonnes towards Mars.

Zubrin himself said a few years ago that SLS was not too dissimilar from what he had in mind.




(around 8:00 mins in)

[Dalhousie]

Mars Direct falls apart once you consider a realistically sized return payload.

No.  In the first iteration of MD the ERV was too small to be practical.  In the second it was not.  The second iteration featured two payloads with landed masses of 40 tonnes, equivalent to a LEO mass of 200 tonnes, well within the 300 tonne LEO capability of a ITS booster without orbital refuelling.  For a similar mass you could also to a MSD mission.  You could almost certainly increase the crew size by 50% and still be within the the payload of the ITS.

But regardless, any "direct" architecture is suboptimal because all launches must be concentrated within one month or so every 2 years.

This is neither correct nor is sub optimal.  For a series of MD or MSD missions of this size you would launch one payload to Mars for the first mission and two for every window (which could be about two months long) thereafter.

[Oli]

Mars Direct falls apart once you consider a realistically sized return payload.

No.  In the first iteration of MD the ERV was too small to be practical.  In the second it was not.  The second iteration featured two payloads with landed masses of 40 tonnes, equivalent to a LEO mass of 200 tonnes, well within the 300 tonne LEO capability of a ITS booster without orbital refuelling.  For a similar mass you could also to a MSD mission.  You could almost certainly increase the crew size by 50% and still be within the the payload of the ITS.

Do you have a link to this second iteration plan?

This is neither correct nor is sub optimal.  For a series of MD or MSD missions of this size you would launch one payload to Mars for the first mission and two for every window (which could be about two months long) thereafter.

Well, fact is you have to build a rocket that is much bigger than necessary (compared to LEO assembly) and is either underutilized (if it launches only twice every 2 years) or requires excessive launch infrastructure (if it, for example, launches 10 times within a window).

[Dalhousie]

Mars Direct falls apart once you consider a realistically sized return payload.

No.  In the first iteration of MD the ERV was too small to be practical.  In the second it was not.  The second iteration featured two payloads with landed masses of 40 tonnes, equivalent to a LEO mass of 200 tonnes, well within the 300 tonne LEO capability of a ITS booster without orbital refuelling.  For a similar mass you could also to a MSD mission.  You could almost certainly increase the crew size by 50% and still be within the the payload of the ITS.

Do you have a link to this second iteration plan?

It's the Zubrin and Weaver (1993) paper http://www.marssociety-europa.eu/wp-content/uploads/2011/10/Near-Term-Mars-Mission-Options_Zubrin_1993_21.pdf

This is neither correct nor is sub optimal.  For a series of MD or MSD missions of this size you would launch one payload to Mars for the first mission and two for every window (which could be about two months long) thereafter.

Well, fact is you have to build a rocket that is much bigger than necessary (compared to LEO assembly) and is either underutilized (if it launches only twice every 2 years) or requires excessive launch infrastructure (if it, for example, launches 10 times within a window).

It's much more efficient to minimise the number of launches.  Multiplying them increases the likelihood of delays. IMHO of course!

WRT to the original question you re SLS could do could MD with two SLS launches for each departing payload.   That's two launches for the initial window and four launches for every window subsequently.

[Oli]

Mars Direct falls apart once you consider a realistically sized return payload.

No.  In the first iteration of MD the ERV was too small to be practical.  In the second it was not.  The second iteration featured two payloads with landed masses of 40 tonnes, equivalent to a LEO mass of 200 tonnes, well within the 300 tonne LEO capability of a ITS booster without orbital refuelling.  For a similar mass you could also to a MSD mission.  You could almost certainly increase the crew size by 50% and still be within the the payload of the ITS.

Do you have a link to this second iteration plan?

It's the Zubrin and Weaver (1993) paper http://www.marssociety-europa.eu/wp-content/uploads/2011/10/Near-Term-Mars-Mission-Options_Zubrin_1993_21.pdf

That plan assumes 45t landed payload for a 72t lander. Note JPL assumed 23t payload for a 75t lander. The best I've seen from NASA is 40t payload for a 85t lander (HIAD).

As for the return payload. 20t total is borderline. A good estimate for a return hab is 25t, without capsule. Orion unfueled weights ~15t, you might get away with somewhat less for a less capable design, but 5t?

Well, fact is you have to build a rocket that is much bigger than necessary (compared to LEO assembly) and is either underutilized (if it launches only twice every 2 years) or requires excessive launch infrastructure (if it, for example, launches 10 times within a window).

It's much more efficient to minimise the number of launches.  Multiplying them increases the likelihood of delays. IMHO of course!

WRT to the original question you re SLS could do could MD with two SLS launches for each departing payload.   That's two launches for the initial window and four launches for every window subsequently.

Minimizing the number of launches is a good way to make these launches as expensive as possible. As for delays, you want to launch 4 SLS within one month? That's a lot more challenging schedule-wise than launching the same payload over the course of 2 years.

[Dalhousie]

Mars Direct falls apart once you consider a realistically sized return payload.

No.  In the first iteration of MD the ERV was too small to be practical.  In the second it was not.  The second iteration featured two payloads with landed masses of 40 tonnes, equivalent to a LEO mass of 200 tonnes, well within the 300 tonne LEO capability of a ITS booster without orbital refuelling.  For a similar mass you could also to a MSD mission.  You could almost certainly increase the crew size by 50% and still be within the the payload of the ITS.

Do you have a link to this second iteration plan?

It's the Zubrin and Weaver (1993) paper http://www.marssociety-europa.eu/wp-content/uploads/2011/10/Near-Term-Mars-Mission-Options_Zubrin_1993_21.pdf

That plan assumes 45t landed payload for a 72t lander. Note JPL assumed 23t payload for a 75t lander. The best I've seen from NASA is 40t payload for a 85t lander (HIAD).

As for the return payload. 20t total is borderline. A good estimate for a return hab is 25t, without capsule. Orion unfueled weights ~15t, you might get away with somewhat less for a less capable design, but 5t?

Well, fact is you have to build a rocket that is much bigger than necessary (compared to LEO assembly) and is either underutilized (if it launches only twice every 2 years) or requires excessive launch infrastructure (if it, for example, launches 10 times within a window).

It's much more efficient to minimise the number of launches.  Multiplying them increases the likelihood of delays. IMHO of course!

WRT to the original question you re SLS could do could MD with two SLS launches for each departing payload.   That's two launches for the initial window and four launches for every window subsequently.

Minimizing the number of launches is a good way to make these launches as expensive as possible. As for delays, you want to launch 4 SLS within one month? That's a lot more challenging schedule-wise than launching the same payload over the course of 2 years.

In your opinion.  Oddly enough, I don't know of any study that supports this.  Do you know of a Mars mission study in the past 50 years that has used launchers with low Earth payloads of less than 50 tonnes and shown that this is superior to using larger boosters I would be most interested in seeing it.

[Robotbeat]

Ignoring "in the last 50 years":

Werner Von Braun's original Mars Project study.

Also, Zubrin's study.

And Skylon's study as well.

Small launchers are superior for small scale human Mars missions because you don't need a dedicated launcher. It also makes a reusable launcher more feasible because the launch rate is higher. That's what makes them superior.

[Robotbeat]

Link to Skylon's Troy Mars mission:
http://web.archive.org/web/20120629090349/http://www.reactionengines.co.uk/downloads/mars_troy.pdf

[Dalhousie]

Ignoring "in the last 50 years":

There is a reason for that proviso - Prior to 1965 we did not know enough about Mars to make a Mars mission resign realistic.

Werner Von Braun's original Mars Project study.

Landmark study, but is 950 launches realistic?  Nope.

Also, Zubrin's study.

The smallest Mars mission proposed by Zubrin I know of was using FH, and that was in little more than an extended email.  FH has a payload of just over 50 tonnes (I chose 50 tonnes for a reason). Link please to anything smaller. 

And Skylon's study as well.

Thanks for the link, I had not seen the paper only the promotional material, which was really making the case for Skylon, not a rational Mars mission 

It's very von Braun-esque, is it not?.   No less that 522 flights and a dedicated station to carry out the mission.  Even if you cut the mission to a third (there are three spacecraft) that is 174 flights by Skylon, plus a dedicated space station. All predicated on  Skylon of course.  Although I guess it could be argued that you could substitute Skylon with anything with similar payload.

Small launchers are superior for small scale human Mars missions because you don't need a dedicated launcher. It also makes a reusable launcher more feasible because the launch rate is higher. That's what makes them superior.

Strawman arguments.  Large launches need not be dedicated to Mars missions.  Using a hundred or more launches to assemble something is not easy, cheap or efficient. High launch rate seems like special pleading in favour of a launch provider rather than a sensible architecture.

There are good reasons why of the almost 100 Mars mission studies I have read or seen summaries of, avoid small launches.