To be sure we're talking about the same thing, here's what I think we're discussing: The depot itself is in HEEO, with a period of a week or two. As a result, it likely only gets a refueling tanker to visit it once per orbit, so ten refuelings would take ten or twenty weeks.
Then there's the question of launching a mission from HEEO. Most likely, it has to rendezvous with the depot at perigee, do a plane change at apogee (since the HEEO is unlikely to be aligned with the mission target), and then do a big Oberth burn at perigee. But is that going to work? Unlike LEO, HEEO precesses rather slowly, so it seems to me that you'd be unlikely to be in the right place with respect to the Earth and the mission target. (The argument of periapsis will be wrong--and expensive to change.)
But couldn't you also get that by just having a second depot in GEO?
I suspect that for many years, and certainly for Artemis, the entire sequence of refueling will be preplanned for a particular mission. The planning works backwards from the final goal, so everything is where you need it then you need it. Depots will not usually be left in HEEO for the next mission, since they will be in the wrong orbit. Depending on design and cost they will either be abandoned in orbit, disposed of by reentry or landed for reuse.
Depots will not usually be left in HEEO for the next mission, since they will be in the wrong orbit. Depending on design and cost they will either be abandoned in orbit, disposed of by reentry or landed for reuse.
To be sure we're talking about the same thing, here's what I think we're discussing: The depot itself is in HEEO, with a period of a week or two. As a result, it likely only gets a refueling tanker to visit it once per orbit, so ten refuelings would take ten or twenty weeks. That could mean passive methods to reduce boiloff won't be adequate, so it'll need active cooling.
The depot will pass through the Van Allen belts over and over and over, so it'll need to be radiation hardened to some extent. The tankers will be exposed to a good bit more radiation as well (two passes each refueling), so they might need to be tougher as well.
you could gather a fleet of ten tankers in LEO and have them burn in formation so they all rendezvous with the depot during the same orbit and transfer the fuel in less than a week
If a depot is able to EDL and re-use, what's the difference between that and a tanker?
Quote from: Barley on 09/05/2023 02:20 amyou could gather a fleet of ten tankers in LEO and have them burn in formation so they all rendezvous with the depot during the same orbit and transfer the fuel in less than a weekTen tankers burning from LEO to HEEO?? Why so many?It's very beneficial to consolidate fuel into one tanker in LEO before delivering it to HEEO. It's quite inefficient to have each individual tanker launch deliver directly to a higher orbit.
Why such a long orbital period? As you yourself point out, making that choice is causing problems for yourself.Do the math on the extra delta-v gained by going from a 48-72 hour orbital period vs 2 weeks. It's only 0.1-0.2 km/s. So by choosing a more pragmatic (shorter) orbital period, effectively the tradeoff is that you "only" get a boost of 3.0-3.1 km/s, vs 3.2 km/s.
So, given that you're willing to expend the depot after a single mission, it does all seem to work. If you want to reuse the depot, though, I think it pretty much has to be in LEO. Do you agree?
I'll just drop a link for Jon Goff's blog post on roving depots associated with HEEO for interplanetary departure, in the context of Jon Goff's 3 burn departure paper, as reference info...https://selenianboondocks.com/2021/02/an-updated-propellant-depot-taxonomy-part-vi-roving-depots/
Quote from: Asteroza on 09/20/2022 11:32 pmI'll just drop a link for Jon Goff's blog post on roving depots associated with HEEO for interplanetary departure, in the context of Jon Goff's 3 burn departure paper, as reference info...https://selenianboondocks.com/2021/02/an-updated-propellant-depot-taxonomy-part-vi-roving-depots/It'd be nice if Jon Goff could weigh in on this discussion, with respect to the HEEO orbital period in light of the sub-2 week option.
A.) It doesn't need to be a specialized depot in HEEO. All you need is a standard tanker to deliver the fuel to HEEO. Afterwards the tanker just deorbits, reenters and gets reused — like normal. B.) Even if you want to use a specialized depot, the depot doesn't have to be expended after a single mission. It can be reused by aerobraking it back to LEO, after (optional) apogee burns to change orbital parameters if needed.
2 weeks seems like a long time. A while back I calculated that 20,000km apogee was good enough (~6 hour period), most of the benefit is gained for the additional deltaV and for Mr Oberth and it's a lot less time to line up orbits for destinations and for refueling.
He talks a lot about "the next time its plane lines up with the low-orbit"... is this based on orbits that naturally precess by a large amount? Is this a significant issue for elliptical earth orbits in the ecliptic plane?
Quote from: InterestedEngineer on 09/06/2023 02:02 am2 weeks seems like a long time. A while back I calculated that 20,000km apogee was good enough (~6 hour period), most of the benefit is gained for the additional deltaV and for Mr Oberth and it's a lot less time to line up orbits for destinations and for refueling.I also get 6 hrs for a 20,000 km altitude, but the extra ∆v is just 2.0 km/s vs. the 3.0 km/s you get for a 2-day period. One kps seems like a lot to me. It also spends 60% of its time in the Van Allen belts, almost all of it in the inner belt.As far as lining up goes, I figure it precesses once every 1.28 years vs. 45 days for a circular orbit 200 km up. To me, that seems like enough precession to be a problem but not enough to be useful.
3km/sec requires a mass ratio of 2.27 which uses 62% of the fuel. You'd have to boost two refuelers to the HEO and that'd have to all be co is ordinated over 2 day orbits. Yikes.
Quote from: InterestedEngineer on 09/06/2023 07:33 pm3km/sec requires a mass ratio of 2.27 which uses 62% of the fuel. You'd have to boost two refuelers to the HEO and that'd have to all be co is ordinated over 2 day orbits. Yikes.IMHO the yikes is completely inappropriate. It's not like navigating a sailboat, where wind and tide are at least somewhat unpredictable. If you do the orbital math right everything ends up exactly where you need it. The math is absolutely trivial compared to every other part of a rocket program, such as finite element analysis, let alone computational fluid dynamics. I am often amazed by how much money and effort engineers will expend to avoid simple calculations.