So is an RFP expected for the PPE? Or does that exist somewhere and I missed it?The latest front page article mentions that the budget proposal indicates that the RFP will ask for the company proposing the PPE design will also commercially source a launch for it.https://www.nasaspaceflight.com/2018/03/cislunar-station-new-name-presidents-budget/
“The targeted release of the draft solicitation will be in the April 2018 timeframe with final proposals anticipated to be due in the late July 2018 timeframe"
But what is the point with LLO really? It adds 1000 m/s of requirements on the Orion(vs NRHO), but subtracts 1000 m/s of requirements from the lander (vs staging at NRHO). The lander can be smaller and lighter compared to Orion that has to re-enter and support crew for longer durations and thus it could very well take less fuel to move the lander an extra 1 km/s vs move Orion an extra 1 km/s
While speculation is fun, I prefer to know what I'm talking about.
I am looking for the thread on ideal Earth orbit transfer points for SEP tugs and search results have failed so far. If no such thread exists, can someone help me identify the homework that needs to be done to justify thread creation? I'm really curious just how much TLI(or any other destination) Dv can be transferred from Earth LVs. 100 km 86° LLO appears to be the best compromise to use for proper exploration of the Lunar poles while allowing access to other points of interest. Fixing the Earth orbit departure point(Please let it be my hypothesized EML1-synchronous elliptical parking orbit with a perigee between 6000-10,000 km.) is required so that I can move beyond speculation about overall architecture mass budgets.
Quote from: Joseph Peterson on 03/08/2018 05:15 amWhile speculation is fun, I prefer to know what I'm talking about.Always a good idea!QuoteI am looking for the thread on ideal Earth orbit transfer points for SEP tugs and search results have failed so far. If no such thread exists, can someone help me identify the homework that needs to be done to justify thread creation? I'm really curious just how much TLI(or any other destination) Dv can be transferred from Earth LVs. 100 km 86° LLO appears to be the best compromise to use for proper exploration of the Lunar poles while allowing access to other points of interest. Fixing the Earth orbit departure point(Please let it be my hypothesized EML1-synchronous elliptical parking orbit with a perigee between 6000-10,000 km.) is required so that I can move beyond speculation about overall architecture mass budgets.I don't understand what you mean by transferring TLI delta-V. But if we're talking about using electric propulsion to get things to the moon, the most efficient thing to do (i.e., the thing that would make most use of electric propulsion and the least use of chemical) would be to shift from chemical to electric in LEO. The delta-V needed for a constant-low-thrust transfer between two circular orbits is simply the difference in the circular velocities of the two orbits. You can think of escape as being a circular orbit at infinity, i.e., one with a circular velocity of zero. TLI is a little bit short of escape, but the difference is not large.The inclination of the lunar orbit has little impact on the delta-V needed. The moon's radius being about 1738 km, the difference between aiming for lunar equatorial orbit and lunar polar orbit at an altitude of 100 km is only about (1738 km + 100 km)/(384,400 km) = 0.00452 radians = 0.259 degrees.
Space Systems/Loral, L.L.C., (SSL) in Palo Alto, California, $2 million Proposal: In-Space Xenon Transfer for Satellite, Servicer and Exploration Vehicle Replenishment and Life Extension
Also launch from Earth is implied NRHO having a few opportunities each month vs L2 having an opportunity every day. So for regular opperations NRHO imposes mission planning/scheduling restrictions.
I understand that NHRO is easy to use to get to other Lunar orbits. It is practically a transfer orbit between HLO and LLO with very small DV to change orbits. But as a more permanent orbit location it has many disadvantages. As discussed earlier it is the fact that it takes less DV from Earth to reach a NHRO than L2 is the probably the main reason it is being picked because of SLS/Orion shortfalls when carrying a co-payload. Also NASA has yet to figure out exact how the DSG will ultimately be used. Use also specifies the orbit. By picking NHRO initially the usage determination can wait until the DSG is actually orbiting around the Moon. 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.
...and we still don't know what Orion SM delta-v is: 1200, 1500 or 1800 m/s ? what is sure is that a) it is inferior to Apollo CSM 2500 m/s and b) if lower than 2000 m/s, it can't enter / exit LLO...
TLI + 450 m/s > to NRHO (uncertain)
TLI + 829 m/s > NRHO (uncertain)
Due to the shutdown, the contract start date has moved to May 31.Also, I found these NAC HEO slides from December which indicate more than one partner may be selected. If that had been mentioned before, then I missed it.