ARM had a docking port for Orion. PPE would just need the one. Right?
Quote from: Propylox on 07/21/2017 03:09 AM"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?
"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.
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.
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.
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-marsIMHO A small spacestation containing 4 tiny modules to be lifted by 4 SLS and assembled by 4 Orions appears excessive.
... 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.
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.
Quote from: oldAtlas_Eguy on 07/22/2017 01:50 AM... 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?
"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 2016https://ntrs.nasa.gov/search.jsp?R=20160003078
Quote from: Propylox on 07/21/2017 03:09 AM"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 2016https://ntrs.nasa.gov/search.jsp?R=20160003078I 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.
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.
Quote from: Endeavour_01 on 07/23/2017 06:25 PMQuote from: Propylox on 07/21/2017 03:09 AM"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 2016https://ntrs.nasa.gov/search.jsp?R=20160003078I 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.
We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outboundtrip times to keep the arrival in and departure from the NRHO near the favorable regions ofthe NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions wouldapproach the performance of the free-phase missions once per NRHO period. At these points nearthe phase match, there would typically be from 3 to 5 consecutive feasible rendezvous missionopportunities, 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 opportunitieseach month, with each set spanning 3 to 5 consecutive days. The results also indicatethat, at least broadly, the previous free-phase results can be used to gain insight into the generalperformance situation for fixed-phase trajectories.
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.
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.
QuoteWe found that in order to minimize Orion propellent usage, the optimizer was adjusting the outboundtrip times to keep the arrival in and departure from the NRHO near the favorable regions ofthe NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions wouldapproach the performance of the free-phase missions once per NRHO period.https://ntrs.nasa.gov/search.jsp?R=20170001352These are launch opportunities with Orion towing a 10 ton module to rendezvous with another object already in that orbit.
We found that in order to minimize Orion propellent usage, the optimizer was adjusting the outboundtrip times to keep the arrival in and departure from the NRHO near the favorable regions ofthe NRHO for those maneuvers. In terms of Orion propellant used, the rendezvous missions wouldapproach the performance of the free-phase missions once per NRHO period.
Quote from: A_M_Swallow on 07/24/2017 02:41 AMI 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.