So I'm still sticking with my original position, which is that this whole emphasis of maneuverability to EML-1 is just a last-minute add-on to try to get the Lagrange nerds on board with the iffy LOP-G project. Political consensus building, and not a real thing to which we can actually look forward.
This is a more basic question: How exactly is the PPE going to perform station keeping? The simplest way to do attitude control on a spacecraft is to have many small thrusters all around and use them to rotate, however the PPE seems to have a single large engine and multiple modules assembled on one side.Will the PPE rotate the entire station before firing the main engine? In this case "orbital changes" and reboost would be it's main capability.
argue against it on the merits of what is being proposed
I'm gonna stick with what is in the RFI
How viable is it to move a spacestation from a near-rectilinear halo orbit (NRHO) to Earth-Moon Lagrange Point 2 (EML-2) and back again every couple of years?The spacestation is likely to mass 40-50tonne and have 40kW available for electric ion propulsion. I do not know what the delta-v from NRHO is but Low Lunar Orbit to EML-2 is about 0.65km/s. Ion thrusters are slow so travel time is important.
Would a facility at EML-1 need constant orbital station-keeping adjustments, or would periodic bursts suffice?
For the LOP-G, it would seem that it is currently envisioned as a way to move the stack to EML-2 to act as a staging point for a journey to MARS!
While orbital mechanics is a beautiful and well-night perfect math, engineering is not and there have been fiction stories about people trying to bring an asteroid to Earth and some engineering cock-up leaves it on an uncontrolled collision course.
What would be far more interesting to me would be if the PPE was proposed as part of a modular orbital transfer vehicle (OTV, to use the SEI parlance) for cargo in cislunar space.
But is it obvious that a permanent facility is needed at the staging point? NASA's Evolvable Mars Campaign, for example, foresees staging in lunar DRO but place no permanent infrastructure there. Given that just maintaining LOP-G is likely to cost over $3 billion per year (just to send one Orion/SLS there annually), it's really not clear to me that LOP-G wouldn't hinder a Mars effort more than it would help.
Neither speaker wants to accept the political reality. LOP-G is modelled on the ISS because the ISS has proven uncancellable. Mankins' concluding remarks are the closest either got to saying that. The goal of LOP-G is to ratchet up the sustainable funding of in-space architecture. If you're a fan of government expenditure on uncancellable space projects, you should be cheering LOP-G, or presenting an alternative that is equally as uncancellable. Zubrin's suggestion of a lunar village as an international project (with Mankins nodding on) doesn't cut the mustard.
Quote from: QuantumG on 08/26/2018 02:22 amNeither speaker wants to accept the political reality. LOP-G is modelled on the ISS because the ISS has proven uncancellable. Mankins' concluding remarks are the closest either got to saying that. The goal of LOP-G is to ratchet up the sustainable funding of in-space architecture. If you're a fan of government expenditure on uncancellable space projects, you should be cheering LOP-G, or presenting an alternative that is equally as uncancellable. Zubrin's suggestion of a lunar village as an international project (with Mankins nodding on) doesn't cut the mustard.Why is an international lunar village more cancellable than LOP-G?