NASA Moon to Mars Architecture: The Mars Segment

[Todd Martin]

First impression of the Mars segment:  They're sticking with the TransHab to Mars, and they're sticking with the assumption that it needs to propulsively capture into Mars orbit, with enough prop to return via an opposition-class orbit.  That's the bad news.

The good news is that, unlike DRA 5.0, which assumed nothing but Ares V-launched cargo pre-positioning missions, they've adopted a wide range of CLV-launched cargo options, and they've left open the possibility that the lander could be either a "flat bed" lander, with crew and payload close to the ground, or a "vertical lander", which is obviously supposed to be a Starship.

The other thing of note is that they're looking even more seriously at short-stay architectures for the first mission.  Short-stay missions overall have shorter total mission time, which is nice from a hardware reliability standpoint, but they have considerably longer transit times, which is bad from a crew microgravity and radiation exposure standpoint.

The conops that goes something like this:

1) Send a whole bunch of surface assets in the synod before, including your surface-to-LMO ascent vehicle.

2) Assemble the DST, whatever it turns out to be, at the Gateway.

3) Push the DST into what they're calling a lunar distance high earth orbit (LDHEO).  Note that this is basically the Artemis NRHO fast return to TEI, but the TEI results in the spacecraft going into something like a 500km x 380,000km HEEO.

4) Crew, via SLS/Orion, does RPOD with the DST in LDHEO.

5) DST, with one of a number of propulsion options  (NEP+chemical, SEP+chemical, NTP, or all-chemical), does a conjunction-class TMI, taking the Orion with them.

6) DST propulsively enters a 5-sol eccentric Mars orbit (HEMO?) and does RPOD with the lander.

7) Lander goes to surface for a ~30day crew stay.

8 ) Crew returns on pre-positioned Mars ascent vehicle, does RPOD with the DST.

9) DST returns on an opposition-class TEI, which may or may not require a Venus flyby to make the Earth arrival speed viable.

10)  Presumably, the crew would then use an Orion to reenter.

One thing I don't understand is why they wouldn't be adopting a long-stay mission (i.e., wait 500days for a conjunction-class return), but have a short-stay oppo-class return as an abort option.  If I ran the circus, and I had a lot of delta-v available (wonder what could provide that?), I'd do the following:

a) Depart in the DST on a conjunction-class orbit with enough energy to do a 2:1 resonance heliocentric orbit with Earth, allowing a free-return to Earth if something went bad in transit.

b) After a go/no-go commit to Mars orbit insertion, insert.  I suspect that with the 2:1 orbit, aerocapture becomes a requirement.  (Direct EDL is not a requirement.)  If no-go, just keep going.  It's a long trip home, but it doesn't require any major propulsion.

c) Do RPOD with the lander (which I really want to call HLS-M).

d) A second go/no-go decision here:  land, or not?  If not, the DST departs within 30days to an oppo-class abort to Earth.  Otherwise...

e) Descend to the surface and its pre-positioned equipment.

f) Do a stay/no-stay decision within the first couple of weeks.  If no-stay, use the Mars ascent vehicle back to the DST and do the oppo-class abort.

g) If staying, you commit to the full 500day stay.

h) 500days later, use the MAV to return to the DST, which then does a conjunction-class TEI.

i) Do direct EDL, using Orion (or something else!).

The caveat to all of this is the "lots of delta-v" requirement.  But we now know how to send (or make) as much prop as necessary to provide copious amounts of delta-v for the mission--as long as Starship works.

Note that, as with the Artemis architecture, all the human stuff is nominally under NASA's control, and nominally finds a way to use at least one SLS/Orion flight to ferry the crew from Earth to LDHEO, where the Orion goes along for the ride and acts as the Earth EDL vehicle.  But also note, just like with Artemis, it's easy to substitute a Starship for a lot of the pieces-parts in here.

Procedural question for the thread:  I'm sure there's a planetary protection food fight in the offing.  I propose the following truce:

A) We all agree that there are huge modifications to Category IV, which will occur, and we don't talk about them here.

B) There are more substantive issues with Category V (protecting Earth from the returning vehicles and crew).  We could spin those off into a separate thread or deal with them here.  IMO:  the core requirement is that the vehicle that does EDL breaks the chain of contact by never having touched the surface of Mars.  Note that Orion is ideal for this, but you could do the same with a Starship that stayed in LMO.

It should be mentioned that Pam Melroy mentioned during her presentation (at 27 minutes) linked below that the objective for Mars is also a continued presence just like the Moon but they didn't want to plan that out just yet as what they will learn on the Moon will have an impact on longer Mars missions.

https://forum.nasaspaceflight.com/index.php?topic=57221.msg2476805#msg2476805

That seems wise of her.

It also seems wise that we concentrate more on early Mars missions here than turning it into yet another "Mars Colony" thread.  This short-stay vs. long-stay issue is a big fat hairy deal.  It's ironic that short-stay is profoundly enabled by Starship's ability to fling propellant at the problem, but that Starship also greatly increases the ability to have a bulletproofed long-stay architecture.

Looking at the Conops presented, I noticed that Orion with its service module is proposed to be taken along with the crew to Mars.  To me, that seems like roughly 5 metric tons of unneeded mass for that portion of the crew trip which slows down the transit time.  I would suggest that one Orion deliver the crew to the Mars Transfer Vehicle and is autonomously returned to Gateway.  A second Orion would be pre-delivered to Mars orbit.  Ideally, that pre-positioned Orion would dock to an orbiting station that could serve as an emergency habitat or staging area, like Gateway.

[Paul451]

Todd, TheRadicalModerate, and yg1968,

Edit your quotes to just the part you are replying to. It's annoying for others to have to scroll unnecessary pages of text.

A second Orion would be pre-delivered to Mars orbit.  Ideally, that pre-positioned Orion would dock to an orbiting station that could serve as an emergency habitat or staging area, like Gateway.

Orion isn't used at Mars. It can't land people on Mars, because there's no way to launch them back to orbit. The normal Mars architecture requires a whole extra Mars lander.

If you aren't taking Orion with you, you don't need to send one to Mars.

[Paul451]

[Starship] is also capable of doing the same job as the nuclear ship anyway.
So what does the nuclear ship actual add that Starship isn't already going to do?

You are forgetting that the US Congressional critters could use a large in space nuclear thermal transport development program in the same way as the SLS. As a pork trough for many Congressional districts. Which the few Starship production sites at CA, FL & TX will not provided.

Forgive me for not seeing "it will make stupid, corrupt people happy" as a good reason.

[Todd Martin]

Paul, the Conops proposed by NASA which we are discussing has Orion first taking crew to the Mars transfer vehicle, then this combined stack goes to Mars.  A separate part of that stack is a Mars lander.  After the Mars surface mission is concluded, the MTV and Orion journey back to earth and the crew uses Orion to land on earth without needing to first enter Earth orbit for rendevous with an EDL craft (Earth Descent and Landing).  What I was proposing is having an Orion pre-positioned in Mars orbit to reduce crew trip time (you can select a faster trajectory with less mass).

A second Orion would be pre-delivered to Mars orbit.  Ideally, that pre-positioned Orion would dock to an orbiting station that could serve as an emergency habitat or staging area, like Gateway.

Orion isn't used at Mars. It can't land people on Mars, because there's no way to launch them back to orbit. The normal Mars architecture requires a whole extra Mars lander.

If you aren't taking Orion with you, you don't need to send one to Mars.
[/quote]

[Paul451]

Paul, the Conops proposed by NASA which we are discussing has Orion first taking crew to the Mars transfer vehicle, then this combined stack goes to Mars.  A separate part of that stack is a Mars lander.  After the Mars surface mission is concluded, the MTV and Orion journey back to earth and the crew uses Orion to land on earth without needing to first enter Earth orbit for rendevous with an EDL craft (Earth Descent and Landing).  What I was proposing is having an Orion pre-positioned in Mars orbit to reduce crew trip time (you can select a faster trajectory with less mass).

Apologies. I assumed you'd misunderstood the reason for taking Orion with the MTV.

However, your alternative still won't provide the advantage you believe:

In order for the Orion to serve its role upon Earth-return, it needs to be able docked with the MTV during the return. Therefore the MTV has to be able to propel its mass along with Orion, from Mars to Earth.

You are only suggesting, therefore, to send Orion separately on the Earth-to-Mars leg. But that requires having another dedicated vehicle for just that leg (SLS isn't good enough to put Orion into MTI, the Orion service module isn't good enough to capture into Mars orbit). Inevitably, IMO, the added cost/propellant/engine-sizing to allow the MTV+Orion to travel to Mars together will be the same or less than the cost/etc of the MTV + other vehicle separately. The MTV has to already be able to do the job in order to allow the Earth-return leg, so you aren't saving anything by splitting the task for the Earth-to-Mars leg.

[Paul451]

Building a large nuke powered in Space transporter with a rotating gravity ring attached could in the distant future allow travel to Ceres or the moons of Jupiter and Saturn.  It could start out by transporting tons of equipment to Mars and use Martian Starships to ferry this to Mars surface.  The Starships could refuel on Mars for ferry duties.  Same as on earth. 
I'm talking about very large that could be built in LEO using Starship earth to LEO ferries.

It seems you are picturing "very large" and thinking it offers some added benefit simply due to its scale.

However:
- A large NTR-propelled ship doesn't enable anything more than its individual components enable.
- Moving those components around the solar system as a single mass is not inherently more enabling than moving them separately.
- The components have to be Starship-launch sized.
- Starship is capable of moving the components around the solar system separately for a lower price than a large NTR-propelled ship.

Therefore:
Anything a large NTR-propelled ship could do (whether it's ferrying supplies to a major Mars base, or exploring Ceres) can be done cheaper and easier with a bunch of Starships.

If you want to go bigger than Starship, for eg, because the components need to be bigger, then you'll also need a bigger launcher to get those bigger components off Earth (and possibly also down to their destination). But now you've developed a bigger, better super-Starship, and the same reasoning applies to moving those bigger components around the solar system: A bunch of super-Starships is able to do anything that a super-NTR is capable of. The super-NTR remains unnecessary.

This only changes when you are no longer supplying most things from Earth. Where the bulk of transport around the solar system is people/material/equipment that originated off-Earth. At that point, large nuclear ships (not capable of atmospheric entry) might start to make sense for some uses, but that's a long way off and not part of the discussion of the "Moon-to-Mars-Architecture".

Similarly, beyond Jupiter, nuclear makes sense (although only as NEP, not NTR.)

But even then, the non-atmospheric ships might still not tend to be bigger than the individual size of the components. "Big" still might not make sense.

I think the "bigger is more efficient" assumption comes from living in an environment with constant drag (road/rail/air/oceans). Orbital mechanics doesn't follow the same rules, so you have to be very careful that you aren't applying assumptions that don't apply in space.


Forgetting "size" for a moment:

The only advantage of NTRs in general is a slightly high Isp than chemical. Which should be enough of a justification on its own. But when you drill into the real-world details, NTRs have such low thrust/weight and add such increased mission complexity, that in practice they don't really offer any benefits over chemical rockets.

...Unless launch is very expensive.

And the whole point of saying "Use Starship to build a big NTR ship" is assuming that Starship is cheap.

The user deltaV gave a perfect example in the Artemis Program Updates thread:

NASA's Mars DRM 5 has nuclear thermal taking 9 Ares Vs vs. chemical taking 12 Ares Vs: https://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf tables 4.1 and 4.2. If you replace expendable Ares V with reusable Starship or New Glenn those 3 extra launches cost a negligible amount compared to the cost of a nuclear thermal program.

[TheRadicalModerate]

Paul, the Conops proposed by NASA which we are discussing has Orion first taking crew to the Mars transfer vehicle, then this combined stack goes to Mars.  A separate part of that stack is a Mars lander.  After the Mars surface mission is concluded, the MTV and Orion journey back to earth and the crew uses Orion to land on earth without needing to first enter Earth orbit for rendevous with an EDL craft (Earth Descent and Landing).  What I was proposing is having an Orion pre-positioned in Mars orbit to reduce crew trip time (you can select a faster trajectory with less mass).

A second Orion would be pre-delivered to Mars orbit.  Ideally, that pre-positioned Orion would dock to an orbiting station that could serve as an emergency habitat or staging area, like Gateway.

Orion isn't used at Mars. It can't land people on Mars, because there's no way to launch them back to orbit. The normal Mars architecture requires a whole extra Mars lander.

If you aren't taking Orion with you, you don't need to send one to Mars.

Stupid, two-part question:

1) Can the Orion CM manage without the ESM if it's hooked up to external power and thermal?

2) How long can the CM support a crew once it's jettisoned the ESM?

All you need the Orion for is to do EDL for the crew in a way that doesn't cost even more capture delta-v, and breaks the chain of contact so that the general public doesn't freak out about Category V Germs From Mars.  As long as you can keep your DST's probability of hitting Earth sufficiently low to satisfy Cat V, you can get really close before cutting the CM loose.

Then the Orion adds less than 11t to the whole DST.

[TheRadicalModerate]

Therefore:
Anything a large NTR-propelled ship could do (whether it's ferrying supplies to a major Mars base, or exploring Ceres) can be done cheaper and easier with a bunch of Starships.

There is a case for NTP other than "move a lot of stuff".  If you have a conops that requires a large amount of delta-v with no ability to refuel, then NTP helps substantially.

NTP doesn't change the fact that things go to hell in a handbasket when mass ratios get much above 6.  But if you're multiplying ln(6) by an Isp that's twice as big as anything chemical, you still get double the delta-v.

This is where short-stay + aerocapture phobia + no refueling starts to make NTP look like a pretty good deal.

That said:

1) I believe that short-stay is an important abort option, but a silly nominal option.

2) The aerocaptophobes need to get over themselves.

3) Even if you don't like the idea of robots mining water, give a robot a tank of LH2 in the synod before you go, and it'll happily turn it into as much methalox as you want.

So it's not that NTP itself is stupid, but the requirements that lead to needing NTP in the first place are stupid.

[Paul451]

This is where short-stay + aerocapture phobia + no refueling starts to make NTP look like a pretty good deal.
[...]
So it's not that NTP itself is stupid, but the requirements that lead to needing NTP in the first place are stupid.

As noted above, even the short stay, non-aerocapture, non-ISRU mission, the chemical-only version required just three more launches than the NTR version. It's still not worth the cost of developing an NTR.

I suspect the same holds true anywhere inside of Jupiter's orbit, at which point NEP so completely outperforms NTR than the latter remains not worth developing.

[TheRadicalModerate]

This is where short-stay + aerocapture phobia + no refueling starts to make NTP look like a pretty good deal.
[...]
So it's not that NTP itself is stupid, but the requirements that lead to needing NTP in the first place are stupid.

As noted above, even the short stay, non-aerocapture, non-ISRU mission, the chemical-only version required just three more launches than the NTR version. It's still not worth the cost of developing an NTR.

I suspect the same holds true anywhere inside of Jupiter's orbit, at which point NEP so completely outperforms NTR than the latter remains not worth developing.

The chemical version in Table 4.2 assumes Mars aerocapture.  If it didn't, it'd be horrific.

[TheRadicalModerate]

A hybrid chemical/NTP option is interesting.  If the NTP can inject the chemical stack into a 2:1 resonant orbit, then cut itself free, it'll wind up back at Earth in two years, with only its own dry mass to capture propulsively back into Earth orbit, where it could be used for the next synod's mission.

The remainder of the stack would have to do some chemical deceleration to be able to do a non-insane aerocapture, but it'd be less than it would have had to provide to do the TMI in the first place.  From there, the conops would be almost the same as the all-chemical conops in the DRM.

This also has the nice property of a short-ish outbound transit time (~130days).  Not only is that easier on the crew, it gives a wider window in which to decide whether to do a full-synod long stay or do the short stay.  And of course the 2:1 orbit allows the crew to do a free return.

[Robotbeat]

It’s a logistics issue. And therefore a cost issue. No mention of NTR for Mars missions should be divorced from a cost analysis using commercial launch capacity like is being used for Artemis.

The benefit of NTR is in reducing launch costs for a given mission delta-v. And commercial launch for Artemis should be calculated as low as $1000/kg IMLEO and possibly lower by the time the mission would occur. From multiple providers, like with Artemis.

A reduction of IMLEO from 2000t to 1500t saves you $500 million. Can the bunch of NTR stages buy their way on at those prices?

Any mission you imagine for NTR can be done with chemical (including a 130 day transfer). The exponential rocket equation may make the chemical one absurdly high mass, but you still need to calculate whether that’s actually making it more expensive or not.

[JohnFornaro]

Well, there is a planetary protection food fight in the offing.  At some point, we have to say it is a dead planet.

Or not.

[Paul451]

At some point, we have to say it is a dead planet.

First we'd have to look.

[Mars scientists frustrate me. They know there's a ticking clock, but they refuse to act like it. They're still acting like they have unlimited time and giving greater priority to things that won't be affected by (or be helped by) a human presence.]

[Slarty1080]

Well, there is a planetary protection food fight in the offing.  At some point, we have to say it is a dead planet.

Or not.

Or perhaps there will be a planetary protection fudge factor: the surface is dead, but maybe there's life deeper underground and it would be easier to send a crew to look for that.

[Mr. Scott]

Well, there is a planetary protection food fight in the offing.  At some point, we have to say it is a dead planet.

Or not.

Or perhaps there will be a planetary protection fudge factor: the surface is dead, but maybe there's life deeper underground and it would be easier to send a crew to look for that.

No it’s not dead…. it’s just pining.

[Slarty1080]

Well, there is a planetary protection food fight in the offing.  At some point, we have to say it is a dead planet.

Or not.

Or perhaps there will be a planetary protection fudge factor: the surface is dead, but maybe there's life deeper underground and it would be easier to send a crew to look for that.

No it’s not dead…. it’s just pining.

No! It's shed it's mortal coil and gone to join the choir invisible...

[Zed_Noir]

At some point, we have to say it is a dead planet.

First we'd have to look.

[Mars scientists frustrate me. They know there's a ticking clock, but they refuse to act like it. They're still acting like they have unlimited time and giving greater priority to things that won't be affected by (or be helped by) a human presence.]

When the clock runs out. The scientists' plans and exclusive access to Mars will be push aside to enhanced the survival and return of crew on Mars. When the first wave of Mars bound Starships with crew leaves Earth orbit.

[Robotbeat]

At some point, we have to say it is a dead planet.

First we'd have to look.

[Mars scientists frustrate me. They know there's a ticking clock, but they refuse to act like it. They're still acting like they have unlimited time and giving greater priority to things that won't be affected by (or be helped by) a human presence.]

When the clock runs out. The scientists' plans and exclusive access to Mars will be push aside to enhanced the survival and return of crew on Mars. When the first wave of Mars bound Starships with crew leaves Earth orbit.

Yeah, there's gonna need to be more compromise, and the most extreme viewpoint on it will not prevail, but it is, of course, in NASA's and SpaceX's interest that good science gets done on Mars.

Even when you get to a city or whatever, etc, they're going to have an interest in making sure good science gets done as that is one of the most important revenue streams for a nascent Mars city.

[Todd Martin]

A quick look at UV (ultraviolet) radiation on Mars per Ames Research Center:  "On present day Mars, the total integrated UV flux over 200-400 nm, is comparable to the Earth’s. However, on Mars the shorter wavelengths contribute a much greater proportion of this UV flux. These wavelength ranges, such as UVC (200-280 nm) and UVB (280-315nm) are particularly biologically damaging.
Dust, if present, contributes substantially to attenuating the UV flux reaching the surface."  In other words, Mars surface as far as I can tell is largely self-sterilizing.  The idea that Earth bacteria are going to propagate across a planet from one (or a few) outposts over a larger land mass than Earth and destroy or contaminate all possible underground reservoirs of Martian bacteria within several human lifetimes is NOT plausible.