Deep Space Gateway Power/Propulsion RFI

[okan170]

ARM had a docking port for Orion. PPE would just need the one. Right?

The RFP specifies 2 IDSS-compatible interfaces.  The single ARM one was on the "rear" of the spacecraft (from which the SEP engines are offset) and the new one is in the "nose" where the grabber mechanism would've been. 

[Propylox]

"Near rectilinear halo orbit" is a non-starter. [...] Dump the circus act for a useful LLO and the electric power and propulsion requirements evaporate, as does funding requirements.

Is part of it about wanting a big SEP project in a post-ARM world?  Back-solving from the tech they want to fund?

I'm all for "a big SEP" to transport propellant and infrastructure from (commercial) LEO to (DSG) LLO, but nothing about ARM or this DSG RFI addresses that. I define "big" as 800 to 1,000 kW and capable of +25mT in a 6mo roundtrip. The 12kW HETs won't cut it so don't need testing.

What use is DSG at LLO when no one can visit it. Orion could make it to LLO but it would be oneway trip.

The problem is Orion cannot enter and then exit LLO, so no infrastructure using Orion will be built or moved there.

The leftover ATV and Shuttle OME re-purposed as Orion's temporary Service Module contains 9mT propellant for ~ 1,350 m/s delta-v and isn't capable of LLO missions. But increasing propellant by 6mT to a wetmass of 32mT is ~ 2,000 m/s delta-v. This is enough for LLO and return with ample capabilities and margin.

I thought low lunar orbits (LLO) were unstable, requiring between 0-400 m/s of station keeping.

Putting the DSG in LLO would make lunar landing much easier.

Some are highly unstable, others entirely stable due to the Moon's mass/gravity distribution.

There's no point building a rocket and capsule to go to the Moon if we're not landing and the lower the staging orbit, the less propellant is required per trip. But this assumes the propellant is delivered via SEP, not chemically like Orion.

7.5 mT is the weight of each module. The current plan is for 4 modules.
https://www.nasaspaceflight.com/2017/04/nasa-goals-missions-sls-eyes-multi-step-mars

IMHO A small spacestation containing 4 tiny modules to be lifted by 4 SLS and assembled by 4 Orions appears excessive.

Especially when a functional 42-day docking berth can be placed in LLO with a single TSTO cargo launch. Just not the design and orbit listed in the RFI - because NASA, of course.

[oldAtlas_Eguy]

4 modules comes to about 30mt total delivered with 4 SLS/Orion flights. It is interesting to note that a single SLS/Cargo flight could deliver all 4 modules at once. If the 5th SLS flight will be in 2026 (New RS25E's) and the 6th flight in 2028. That makes the DSG fully functional for use NET 2026 when the first habitat module is delivered. 2 SLS flights prior to the DSG habitat delivery (5th SLS flight) is the Europa Clipper flights (SLS #2/3 and #4). If the EC Lander is delayed then the Habitat could be 2 years earlier but would also require a human rated habitat to be completed/developed in 6 years from now. That is really pushing it since the habitat has yet to even be on contract, not even close to a PDR point (probably at least 3 years away 2020) , CDR a year latter (2021) then 3 years to build and certify the habitat (2024) then a year later launch (2025). So SLS flt #4 could be as late as 2025 if EC#2 (Lander) development is delayed into second half of 2020's.

But to get all 4 DSG modules in orbit could be as late as 2030.

But this PPE design is useful for other uses than just the DSG. So it may have a life of it's own regardless of SLS/Orion or even DSG.

[Propylox]

... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.

I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

[ncb1397]

If the EC Lander is delayed then the Habitat could be 2 years earlier but would also require a human rated habitat to be completed/developed in 6 years from now. That is really pushing it since the habitat has yet to even be on contract, not even close to a PDR point (probably at least 3 years away 2020) , CDR a year latter (2021) then 3 years to build and certify the habitat (2024) then a year later launch (2025). So SLS flt #4 could be as late as 2025 if EC#2 (Lander) development is delayed into second half of 2020's.

Boeing was selected as ISS prime contractor in 1993 and Unity was launched 5 and a half years later in December 1998. If they select one or two of the NextStep Hab partners(Boeing, SNC, Bigelow, Lockheed Martin or Orbital) in 2018, they have a reasonable shot of launching it is 2024 which would be 6 years later. Probably helps the schedule that we have basically been through this rodeo before.

[okan170]

... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.

I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

Calm down, NASA will still be around for you to hate for some time.     Also I'm not sure "Any sort of mission won't be occurring from that orbit" just because you feel that way and dislike the idea.  There are a few missions planned so far, theres no physical reason why they won't happen.

[A_M_Swallow]

... But this PPE design is useful for other uses than just the DSG.
So it may have a life of it's own regardless of SLS/Orion or even DSG.

I'd counter this PPE may have a thousand uses, but DSG ain't one.
Manned habitation, docking attempts, or any sort of mission won't be occurring from that orbit. Meaning DSG will be somewhere else while PPE floats about. If/when DSG is planned for a useful orbit, the electric propulsion system this PPE sports won't be necessary or wanted. Meaning this PPE won't be part of DSG, though that's how NASA is selling it. You buying?

Supplying a 30-40 tonne spacestation with 400 m/s of station keeping per year is going to require a significant amount of thrusting. A propellant depot and lander will significantly increase the mass.

Turning a second PPE into an Isp 4,190 space tug is fairly easy. Low thrust LEO to LLO is a delta-v of 8.0 km/s one way.

A Masten and ULA Xeus reusable lander should be able to land Moon base modules, rovers and with a capsule people.

[JazzFan]

Will the Power/Propulsion module be a clean sheet design or use an existing bus or propulsion module as a foundation to build upon?

[Archibald]

Don't feed the troll...

[oldAtlas_Eguy]

Literally this PPE is a "DEEP SPACE TUG". It has advanced docking adapters for in-space attachment of any "payload" and sufficient DV to push some significant sized items around. As I said before and probably is the reason NASA wants to build it in the first place is that this PPE has a multitude of uses outside of just the SLS/Orion/DSG program. Also with its fore and aft docking it can be stacked with multiple PPE to create a very large outer planetary DV delivery system. Think of mating this PPE to a dedicated Europa Lander. This then makes the EC Lander a simpler design such that the power and propulsion is designed leaving only the communication and experiment packages. Also if this vehicle was to also have a significant communication relay capability then the payload no longer need that either. This module then becomes if used to send stuff to Mars a orbital communication relay with its very high power solar arrays capable of multiple high data rate channels for multiple ground assets and links to Earth. 24KW is 2X the power used on HTS comm sats.

Added:
A question then is the intent to make this PPE have a diameter when stowed such that it could fit in a 5m fairing? If so then it definitely has a future for use in the planetary programs. Much less any HSF programs that eventually get approved regardless of SHLV that is used in that program.

I like this vehicle. It shows some forethought into a "LEGO" in-space methodology. Many have thought that the customized each vehicle method has always been the wrong way to go for shortening the development time and development costs. A more "LEGO" approach where stuff is just docked together on the ground at launch or even in-space docking using smaller LV's gives a large set of options for programs to choose quicker and lest costly development paths. This will also help the DSG in that it offloads much of the design problems of the DSG into logical "LEGO" pieces that can be individually tested and improved/replaced if needed.

[Endeavour_01]

"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.

[oldAtlas_Eguy]

"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.

The one distinct advantage of L2 is that launch windows to that destination are not overly complex. But NRO's require specific timing of the object in the NRO with the Earth's rotation which could be highly restrictive. But for SLS that is unlikly to launch more than once a year that is not really a concern. But for an active continuously manned DSG where commercial services are resupplying and possibly even delivering crews such orbits would represent significant launch scheduling conflicts and other possible lengthy delays when a window is missed.

[A_M_Swallow]

Literally this PPE is a "DEEP SPACE TUG". It has advanced docking adapters for in-space attachment of any "payload" and sufficient DV to push some significant sized items around. As I said before and probably is the reason NASA wants to build it in the first place is that this PPE has a multitude of uses outside of just the SLS/Orion/DSG program. Also with its fore and aft docking it can be stacked with multiple PPE to create a very large outer planetary DV delivery system. Think of mating this PPE to a dedicated Europa Lander. This then makes the EC Lander a simpler design such that the power and propulsion is designed leaving only the communication and experiment packages. Also if this vehicle was to also have a significant communication relay capability then the payload no longer need that either. This module then becomes if used to send stuff to Mars a orbital communication relay with its very high power solar arrays capable of multiple high data rate channels for multiple ground assets and links to Earth. 24KW is 2X the power used on HTS comm sats.

Added:
A question then is the intent to make this PPE have a diameter when stowed such that it could fit in a 5m fairing? If so then it definitely has a future for use in the planetary programs. Much less any HSF programs that eventually get approved regardless of SHLV that is used in that program.

I like this vehicle. It shows some forethought into a "LEGO" in-space methodology. Many have thought that the customized each vehicle method has always been the wrong way to go for shortening the development time and development costs. A more "LEGO" approach where stuff is just docked together on the ground at launch or even in-space docking using smaller LV's gives a large set of options for programs to choose quicker and lest costly development paths. This will also help the DSG in that it offloads much of the design problems of the DSG into logical "LEGO" pieces that can be individually tested and improved/replaced if needed.

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

[ncb1397]

"Near rectilinear halo orbit" is a non-starter. If you'd like to know more about the impossibility of station keeping, manned habitation and severe constraints on every mission plan it creates, NASA has plenty of papers - oddly pointing this out and concluding we should do it anyways. Much like the terrible idea of "Lagrange Gateways" that's been floated for years, now NASA pushes an even worse idea.

Cislunar Near Rectilinear Halo Orbit for Human Space Exploration - Sept 2016
https://ntrs.nasa.gov/search.jsp?R=20160003078

I was only able to read the abstract of that paper but from what I read it doesn't seem that the authors are declaring NRO orbits impossible or worthless. They are pointing out that NROs have never been used for human exploration and that different orbital models will be required. It's a challenge but not an impossible one.

Attached is another paper that I ran across in NSF a while ago that is quite positive on the usage of NROs for human exploration.

The one distinct advantage of L2 is that launch windows to that destination are not overly complex. But NRO's require specific timing of the object in the NRO with the Earth's rotation which could be highly restrictive. But for SLS that is unlikly to launch more than once a year that is not really a concern. But for an active continuously manned DSG where commercial services are resupplying and possibly even delivering crews such orbits would represent significant launch scheduling conflicts and other possible lengthy delays when a window is missed.

Not true...

We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outbound
trip times to keep the arrival in and departure from the NRHO near the favorable regions of
the NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions would
approach the performance of the free-phase missions once per NRHO period. At these points near
the phase match, there would typically be from 3 to 5 consecutive feasible rendezvous mission
opportunities, with the best approaching the performance of the free-phase cases (see Figure 13).
For the short stay missions examined, this means that there would be multiple sets of launch opportunities
each month, with each set spanning 3 to 5 consecutive days. The results also indicate
that, at least broadly, the previous free-phase results can be used to gain insight into the general
performance situation for fixed-phase trajectories.

https://ntrs.nasa.gov/search.jsp?R=20170001352

These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.

[Jim]

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

NASA is paying for the development of a SEP tug, that is what PPE is.

[DreamyPickle]

Isn't it a rather *small* SEP tug at 7500 kg? Launching it together with an Orion puts some severe limitations on it.

Also, isn't the whole point of a SEP tug to move payloads around? I'd expect a real tug to continuously carry payloads from LEO, perhaps synchronized with cargo flights. But it seems the plan is for this to sit in the same orbit for years.

I'd rather describe this as a small space-station core module, providing power and station-keeping.

[okan170]

Isn't it a rather *small* SEP tug at 7500 kg? Launching it together with an Orion puts some severe limitations on it.

Also, isn't the whole point of a SEP tug to move payloads around? I'd expect a real tug to continuously carry payloads from LEO, perhaps synchronized with cargo flights. But it seems the plan is for this to sit in the same orbit for years.

I'd rather describe this as a small space-station core module, providing power and station-keeping.

It has to be able to move between different orbits to support different objectives.

[Propylox]

We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outbound
trip times to keep the arrival in and departure from the NRHO near the favorable regions of
the NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions would
approach the performance of the free-phase missions once per NRHO period.

https://ntrs.nasa.gov/search.jsp?R=20170001352
These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.

Fantastic. This implies there are a few opportunities each month to descend to the surface or to schedule a return from the surface. If there's a surface emergency, they'll just have to die waiting for orbital alignment. If an emergency arises while in orbit, can we safely say only half the orbit allows direct to Earth-return. The other half is also death? Great plan.

[DreamyPickle]

Perhaps I was too quick to dismiss this. But I'm having trouble evaluating how well this would work if used as an actual SEP tug between LEO and NRHO. I can't even find good numbers for the required delta-V to reach NRHO using low thrust maneuvers, is ~8 km/s from wikipedia OK?

Assuming a 500kg adaptor, 5000 kg dry mass and 9000 ISP you need to reserve ~500 kg fuel for a trip back and the remaining ~1500kg is enough to send ~10tons to the moon. This is from some quick excel math, hope I'm at least in the right ballpark.

Such a payload is on the low end of EELV-to-LEO capabilities but that's not necessarily bad if you want cheap cargo. But ideally you would want a SEP tug capable of transferring payloads as large as you can place in LEO, right?

[A_M_Swallow]

I cannot see any mention of the fairing size in the RFI. So if an aerospace firm can design the PPE to fit into a 5m fairing they may get NASA to pay for development of their SEP tug.

NASA is paying for the development of a SEP tug, that is what PPE is.

Correct. I have met salesmen and company directors who think because it is called a PPE that the machine cannot also be a SEP tug. They would expect the second machine to be designed from scratch.