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.
Quote from: ncb1397 on 07/24/2017 05:43 pmQuoteWe 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. 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.
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.
NRHO gives DSG days over one pole per orbit allowing for direct line of sight into that poles craters for hours if not days. Ideal for communicating with assets (rovers, landers) in those craters and maybe beaming power using laser. NRHO is just one of few orbits that DSG can use, between Orion missions it can shift to another.
1) But I'm having trouble evaluating how well this would work if used as an actual SEP tug between LEO and NRHO. Assuming 9000 ISP (snip)2) But ideally you would want a SEP tug capable of transferring payloads as large as you can place in LEO, right?
A delayed Mars program means that Lunar surface becomes a higher priority and with LLO being more desirable, although the same could be said for L2 but that depends on the lander hardware designs used. An accelerated Mars program would make L2 a desirable orbit.
--- continued on ion architecture ---Unfortunately there's only assumptions and hurdles with high-power applications for all three ion options mentioned. The PPE is a puny design, both in power levels and capabilities, that doesn't address any current and future needs or advance technology that is needed. And that orbit. - HET: Material science currently limits cathodes to around 30-50 amps without rapid degradation. It's why I suggested a variable voltage to use high amps/thrust deep in gravity wells and plane changes, then switch to high voltage/isp for spiraling. This preserves the engine, increases efficiency and transit time.Additionally a grid, or cluster of multiple HETs arc across each other, rapidly destroying one at a time. PPE uses broadly-spaced, low power HETs to avoid this while tests have used external magnetic containment poles to isolate each HET. Packing 20-30 HETS of 30-50kW together for a viable SEP tug seems highly problematic. - VASIMR: Weight and reliability are the major questions. This architecture requires active cooling - possibly regenerative, but that may not be enough. If not there's additional system weight and reliability questions.VASIMR's also never done long-duration testing like was planned aboard ISS to prove reliability. This may be a great design, but final operating parameters and design needs to be proven. - HiPEP: While ~9,ooos isp and ~40kW was shown, the efficiency study I linked was to test at up to 16kW for a 25kW mission, but never neared that. It focused on temperatures, coupling, efficiency and degradation around 1kW. I'd guess a final design wouldn't be near 9,ooos by increasing kg/s to keep it cool and reliable.
{snip}4) Adding some TDRSS comm system items to the PPE would increase its usefulness for many missions in the future. Such as a comm relay system for far side of the Moon surface missions. But this also adds those pesky large antennas.
This sounds like more of a 5 year development program than just a 3 year build program. In a three year build program as being requested (delivery date of 2021 and contract start sometime in FY2018), there is no time to develop technology.
With 2 IDSS in requirement, plus SEP... how that will be configured?Assuming SEP on the long-axle, and 1st IDSS on the other end, that will make 2nd IDSS mounted on the side?How that translated to center-of-mass for station keeping boost? SEP on gimbals?Attached image is from Orbital ATK's concept video, which have 2 IDSS on 2 end of long-axle. Small thrusters next to one of IDSS, which doesn't seem functional when that IDSS been used.Or we gonna see Orbital ATK MEV-style HET mounted on extended arm? Which I think is a smart design to somehow adjust the thrust alignment by moving extended arm.Titus
BL's copy of the RFI - #7: These berthing locations will support unpressurized logistics ... and #9b: The PPE will provide a minimum translation path for EVA.I'm assuming that's a tunnel for unpressurized cargo, possibly large enough to pass through or am I misinterpreting "translation path"?
Its the last one you described. Per the renderings from NASA which match the last version of the ARM bus, the SEP thrusters are mounted on moveable arms around the IDSS port (for ARM, Orion was to dock at this port) but most of the gateway seems to be set up to be on the other end of the bus giving it a more traditional-looking configuration. I did a quick render here to show the arrangement in the aft compared with the (more exposed) CAD diagrams of the area from NASA. I do not know if the bus is pass-through (basically a tunnel, like Cygnus DS) or if the IDSS ports are just hard points for moving it around using any compatible vehicle- I'm leaning towards just hard points though simply because I cannot find any information about a tunnel in the design. There is some word of a small science airlock at the "front end" of the bus, but thats from much earlier international discussions and not any NASA documents.