Another way of combining benefits of SEP and hydrazine could be to place a series of propellent depots in your path, such that after you expend the propellent of one you are positioned to rendezvous with the next.I can't find the original thread which had several variations, but I found a summary:SEP accelerated hydrazine depotsIt isn't a serious proposal. If you miss your window or any of the following depots all that effort is wasted. Interestingly though you would not be stranded in space. After each burn you are still on a one year trajectory back to earth. Similarly all your SEP depots could return to aerobrake back into LEO for refueling one year later. (It has some other issues too though.)
3) Hypergolics have terrible isp, but they can be stored for a very long time without boil off issues and are much more dense than LH/LOX systems.
This idea seems to presuppose a large advantage can be gained by moving mass up Earth's gravity well using SEP. I suggest that this step can be much more easily accomplished using hydrolox upper stages of launch vehicles to get to an orbit like super-sync GTO, and then a small hypergolic (or even solid) kick stage to circularize there..
Any numbers to put it into perspective for a layman like me?
This idea seems to presuppose a large advantage can be gained by moving mass up Earth's gravity well using SEP. I suggest that this step can be much more easily accomplished using hydrolox upper stages of launch vehicles to get to an orbit like super-sync GTO, and then a small hypergolic (or even solid) kick stage to circularize there, or maybe even push out into a larger ellipse. At that point, sure, SEP is your "slow boat" friend to move onto trajectories which use three-body (Earth, Moon, spacecraft) dynamics to get you where you want to go.That much is all possible with today's technology. You then "only" need to design your mission architecture so the pieces rendezvous and aggregate in one of the places in the Earth-Moon system where trajectories lead to and from ... anywhere. The frequently discussed possibilities include the colinear Lagrange points and distant retrograde lunar orbits.Was this the kind of architecture you had in mind, or were you planning on the long spiral out from LEO using SEP?
That's why I put the thread in the Moon section. I don't think this would be a good way to go to Mars, except for some cargo.
Unless you use SEP to put heavy radiation shielded closed loop life support artificial gravity cyclers into their correct orbits...this solves some problems, but you couldn't avoid needing a large chemical stage to boost the crew to meet the cycler. I won't touch how you solve that problem with 50 light year clown pole!
Quote from: Darkseraph on 03/20/2015 07:05 pmThat's why I put the thread in the Moon section. I don't think this would be a good way to go to Mars, except for some cargo. It would be excellent for prepositioning propellant to SM-1/2, LMO and perhaps L1/L2, which would be very practical for Mars.
I'd like to see an architecture made from this. I suppose the first starting point is establishing the delta-v needs along with the number of flights.Let's assume there are two key staging points: LEO and L1 (L2 could be another possibility, but most of its benefits are for interplanetary flights). The delta-v for a one-way trip from one to the other is 3.8 km/sec, 7.6 for a round trip. From L1 to the lunar surface, the d-v is 2.5, 5 for a complete trip to-from L1 and the Moon. We have two groups of numbers to work with: 7.6 km/sec for Earthly vehicles and 5 km/sec for Lunar vehicles.The Earthly vehicles consist of the SEP tug and Orion. The Orion's true strength comes from the SLS and returning directly to Earth via reentry. The SEP has a hard job ahead, pushing cargo under its own power from LEO all the way to L1, then slowly returning back to Earth. The SEP would rendezvous with objects largely in LEO, whereas the Orion rendezvous at L1.The Lunar vehicles would be either cargo or crew landers. The cargo variant would have the least amount of fuel of any vehicle, as it would only journey down to the Moon once whereas the crew version needs to return to L1. Neither would deal with Earth's gravity well, as the SEP tug would shove both to L1 and do the hard work for them. The crew lander, between missions, would wait at L1, get refueled by another SEP visit, and then another Orion on its second mission.
The SEP cannot use the Oberth effect so the LEO to EML-1 delta-v is 7.0 km/s, round trip 14.0 km/s. SEP can still be used but it takes longer and needs much more propellant.Direct reentry from EML-1 is 0.77 km/s.The burn between LEO and EML-1 can be performed by the Orion's service module. Larger fuel tanks will be needed than the service module currently being developed or Orion could pick up drop tanks at the LEO spacestation.
Every time a SEP tug goes fro LEO to L1 its solar panels a degradated by approx 20%
Quote from: TrevorMonty on 08/05/2015 09:21 amEvery time a SEP tug goes fro LEO to L1 its solar panels a degradated by approx 20%Can you provide a citation for that?
Quote from: Burninate on 08/10/2015 07:31 amQuote from: TrevorMonty on 08/05/2015 09:21 amEvery time a SEP tug goes fro LEO to L1 its solar panels a degradated by approx 20%Can you provide a citation for that?http://www.iepc2013.org/get?id=045With each one-way trip from earth orbit to a distant retrograde orbit or a destination such as EML2, thespacecraft must pass through the Van-Allen radiation belts. Each pass through the belts reduces the solar arrayoutput by approximately 12% (possibly more, depending on the cover-glass thickness and solar array type).Increasing the solar array size is an obvious work-around to this issue, but since a single re-use of a SEP spacecraftwould require an additional two trips through the Van-Allen belts, the requisite increase in solar array size canbecome a major design driver.LEO - L2 =88%L2- LEO = 77%LEO - L2= 68%
LEO - L2 =88%L2- LEO = 77%LEO - L2= 68%
Quote from: TrevorMonty on 08/10/2015 08:57 amLEO - L2 =88%L2- LEO = 77%LEO - L2= 68%That seems a bit excessive. I've come across the graphs below in a paper from 2007.Note that according to this even a planar 300kw array with 30mils shielding would weight "only" 6t. (SLA stands for "stretched lens array")
Quote from: TrevorMonty on 08/10/2015 08:57 amLEO - L2 =88%L2- LEO = 77%LEO - L2= 68%That seems a bit excessive. I've come across the graphs below in a paper from 2007.
But we have performed landings on the moon using hypergolics and we have transferred propellant this way in space on the ISS. In space refueling with hypergolics is a mature technology and doing reusuable single stage on the moon is much easier than earth.
Quote from: Darkseraph on 03/07/2015 06:02 pmBut we have performed landings on the moon using hypergolics and we have transferred propellant this way in space on the ISS. In space refueling with hypergolics is a mature technology and doing reusuable single stage on the moon is much easier than earth.A small but obvious nitpick : its 'mature technology' in Russia. On US side, still developing
A small but obvious nitpick : its 'mature technology' in Russia. On US side, still developing