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#140 by Bob the Avenger on 23 May, 2009 20:43
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Back to the question I asked, I'm a bit surprised nobody's been able to help out on the low-thrust trajectories issue. I'll keep googling, but a lot of it goes over my head...
The answer to your question is beyond my limited orbital mechanics fu, but while googling I found something called Edelbaum's equation.
Dv=sqrt(v_0^2 + v_f^2 - 2v_0*v_f*cos(i*pi/2))
v_0 would be the Earth's velocity around the sun, v_f the velocity of Mars around the sun, and i any inclination change.
This should give you the delta-v from Earth C3 to Mars C3.
Can any experts comment?
If this is the formula I think it is, its only actually half the manouver. It looks like the formula to find the first deltaV in a Hohmann transfer orbit, although given the day I'm having I might be wrong. Wikipedia has more information on Hohmann tranfer orbits than I can easily explain.
With this sort of problem though, the transfer orbit is only half of it; to leave the Earths orbit around the Sun with a velocity greater than the Earth's you need to use a hyperbolic escape orbit with an excess velocity equal to what you need to leave the Earth's orbit with. Then you have a similar problem when you get to Mars.
I might have misunderstood something and so all of this is probably wrong (its been one of those days). -
#141 by mmeijeri on 23 May, 2009 22:21
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The document I took this from was about low-thrust trajectories. The 6 km/s should only refer to the delta-v to go from Earth C3 to Mars C3. To that should be added LEO->Earth C3 and Mars C3->LMO, but I think Kaputnik was considering doing that with chemical propulsion.
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#142 by Kaputnik on 24 May, 2009 13:12
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The document I took this from was about low-thrust trajectories. The 6 km/s should only refer to the delta-v to go from Earth C3 to Mars C3. To that should be added LEO->Earth C3 and Mars C3->LMO, but I think Kaputnik was considering doing that with chemical propulsion.
Hmmm, this is complicated stuff.
Are you sure you need to find 6km/s? The wiki delta-v chart shows 0.6km/s for that manoeuvre, but presumably using a single impulse.
Actually, what I'd originally been looking for was more about the LEO-C3 aspect. I think this generally requires about 4km/s on a single impulse trajectory, and is a hefty mass penalty for any interplanetary mission. So I was looking for information on how we can use low-thrust high-isp systems to spiral away from LEO instead- whilst not getting fried at the VA belts, or taking years to do it. -
#143 by mmeijeri on 24 May, 2009 13:27
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Hmmm, this is complicated stuff.
I agree.
I'm still wrestling with the basics.QuoteAre you sure you need to find 6km/s? The wiki delta-v chart shows 0.6km/s for that manoeuvre, but presumably using a single impulse.
The 0.6 km/s is for Earth C3->Mars transfer. Mars transfer->Mars C3 is 0.9 another km/s. I take it these are the two impulses for a Hohmann transfer.QuoteActually, what I'd originally been looking for was more about the LEO-C3 aspect. I think this generally requires about 4km/s on a single impulse trajectory, and is a hefty mass penalty for any interplanetary mission. So I was looking for information on how we can use low-thrust high-isp systems to spiral away from LEO instead- whilst not getting fried at the VA belts, or taking years to do it.
The TU Delft link given by Archibald says LEO->C3 takes 5.8-7.4 km/s for SEP, depending on thrust and 3.2 km/s for an impulsive trajectory. Are you thinking about cargo or crew? Because crew could easily stage at L1. -
#144 by Kaputnik on 24 May, 2009 13:33
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You'd keep the crew on the ground up until everything was ready at the rendezvous point- whether this is a high orbit, or a lagrange point, is up to cleverer people than me. The send them in something like an Orion+DHCSS so they don't linger in the VA belts. This 'taxi' concept is well laid out in JPL's study of an AG-NEP Mars architecture.
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#145 by mmeijeri on 24 May, 2009 13:34
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Yeah, that was what I was thinking of.
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#146 by Hop_David on 24 May, 2009 20:16
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Much better (and colourful!) than wikipedia
http://www.clowder.net/hop/railroad/deltaveemap.html
More delta-vee numbers for various locations
(note : It is beyond my understanding that GEO takes 3.8 km/s while Earth escape is 3.2 km/s only
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Thank you for linking to my delta vee map! In my figures the delta vee for for reaching GEO includes a circulization burn at apogee. Some caveats: My figures assume circular coplanar orbits and so are a rough approximation. Also LEO is an ambiguous term. It can be any orbit from earth's surface to 2000 km up, with any inclination. In my models it is an equatorial, circular orbit 300 kilometers above the earth's surface. -
#147 by Hop_David on 24 May, 2009 20:42
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Where can we get reliable (scholarly) information on launch windows, journey times and total mission durations for human Mars missions? From Wikipedia it appears that the minimum energy launch window is about every 2.135 years (780 days)
I have made a spread sheet for Hohmann launch windows:
http://www.clowder.net/hop/railroad/Hohmann.xls
You type departure and destination planets into colored cells. You can also enter apoapsis and periapsis of planetary parking orbits you're departing from and arriving at. The sheet returns launch windows, trip times, and delta vees.
The spreadsheet assumes circular, coplanar orbits. So it's an apprximation.
Is it reliable and scholarly? My most impressive credential is graduating in the top 60% of my high school class. I do make misteaks. If anyone finds wrong assumptions or errors in my spread sheet, I'd appreciate a heads up. -
#148 by Archibald on 06 Jun, 2009 19:28
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I want to compare Zubrin's Athena "double flyby" with Sun-Mars L1/ L2 alternatives.
http://forum.nasaspaceflight.com/index.php?topic=1337.0
http://forum.nasaspaceflight.com/index.php?topic=13532.0
[…] to get to L2 you are initially targeting a close pass of the Moon. At perilune you do a small DV to reduce your orbital energy relative to the Moon, then you coast out to L2 and finally do an insertion burn at L2. It is this "powered lunar swingby" that is the whole secret to the DV advantage of L2 over L1 (3.3 km/s Vs 3.8 km/s)
Do you think we can apply such manoeuvre to a Mars (or Venus!) mission ?
Something like
1- approach on a hohman orbit
2- powered martian swingby
3- enter halo orbit around Sun-Mars L2 with minimal delta-V
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#149 by Hop_David on 07 Jun, 2009 07:54
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I want to compare Zubrin's Athena "double flyby" with Sun-Mars L1/ L2 alternatives.
http://forum.nasaspaceflight.com/index.php?topic=1337.0
http://forum.nasaspaceflight.com/index.php?topic=13532.0
[…] to get to L2 you are initially targeting a close pass of the Moon. At perilune you do a small DV to reduce your orbital energy relative to the Moon, then you coast out to L2 and finally do an insertion burn at L2. It is this "powered lunar swingby" that is the whole secret to the DV advantage of L2 over L1 (3.3 km/s Vs 3.8 km/s)
Do you think we can apply such manoeuvre to a Mars (or Venus!) mission ?
Something like
1- approach on a hohman orbit
2- powered martian swingby
3- enter halo orbit around Sun-Mars L2 with minimal delta-V
The Earth Moon L1 and L2 points are about 84% and 116% of a lunar distance. A normal orbit at L1 altitude would travel about 1.1 km/sec wrt earth. But since L1 moves at the same angular velocity as the moon, it's only going about .85 km/sec. The difference between ordinary orbits and these L points are dramatic!
The Sun-Mars L 1 & 2 points lie about 1.08 million kilometers from Mars. These are about .5% of the Mars distance from the sun. Since these orbits are going the same angular velocity as Mars, they are moving 99.5 and 100.5% of Mars velocity wrt the Sun.
But I will plug in 1.08 million kilometers into Mars apoapsis with 300 km as Mars periapsis.
Coming in from an earth Hohmann, a .7 km/sec burn at Mars periapsis would drop the apoapsis to 1.08 million km apoapsis. Perhaps some of that .7 km/sec could be accomplished with aerobraking.
The natural circular orbit at this altitude would be about .2 km/sec (if there were no sun to perturb it). At periapsis the payload orbit is moving about .016 km/sec. A .184 km/sec circulization burn would be needed if this were an ordinary orbit.
But the L1 point is moving 0 km/sec wrt Mars. So a .016 km/sec burn would suffice to park it there.
So leaving Earth Mars Hohmann to Sun Mars L1 would take (.7 + .16) km/sec. Or about .9 km/sec.
To launch a payload from Mars to the Mars Sun L1 would take about 6 km/sec.
To launch a payload from Deimos to Mars Sun L1 would take about about .6 km/sec. About .9 km/sec for Phobos.
I think. Take what I say with a grain of salt. -
#150 by Archibald on 07 Jun, 2009 17:52
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Thank you very much !Quote
I think. Take what I say with a grain of salt.
Understood. Others posters there will critic these numbers better than I...
In the athena paper Zubrin tell us thatQuoteThe crew will approach and depart Mars twice with
a hyperbolic velocity of about 4 km/s.
How much delta-V is this ? How does this compare to SML-1 / SML-2 mission profiles ?
I had this idea of two identical Athena spaceships flying to Mars in convoy (a la Von Braun Mars 1969 expedition).
They would ride in space above a Jupiter 232 / 246 or an Ares V. A single launch should be enough - Athena fit into a single Energia booster.
When arriving at Mars one would go into a "double flyby" path, the other into a halo orbit around SML-2.
Both would be +/- 1 million kilometer away from Mars.
Just a random thought.
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#151 by Jim on 23 Jun, 2009 15:58
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What is the current status of
a) VASIMR
b) Nuclear Reactor Rockets?
c) Antimatter Catalyzed Micro Fission/Fusion?
B&C have no work being done. -
#152 by nooneofconsequence on 24 Jun, 2009 01:18
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1. What should be done in order to put Man on Mars within the next 10 years (before 2020)?
1. Convince more than 50% of the population in Europe, US, Russia, China, ... that it's necessary for all of us to either/or survive as a species and/or do well economically as a world.
2. Should NASA and ESA co-operate?
3. Should we still use chemical propulsion?
...
Currently, according to CBO research grants for universities the mantra is "we will make you wealthy". Back in the 60's, it was "we will make you safe" ala the Cold War, which is how Apollo was funded as a proxy war with the Soviets.
2. With the election of Obama, there's been a sea change in the desire for international partnership. However, it takes more than desire - the prior administration dismantled most international partnerships, so the US could be a more effective bully - er, able to "act unilaterally". There is still too much sentiment to wind down the ISS as an unsuccessful experiment in international cooperation.
It's incredibility subjective the hundreds of different perspectives I've heard on international cooperation including the ISS. Not everybody likes it. What you have to remember is that when government gets involved, the elements of political dealmaking (like sausage making) is a bit awkward/ugly/cumbersome/inexplicable/inefficient/... I could go on, but its just the way it works.
Now multiply the governments involved ... add more for situational instability and additional geopolitical agenda "pay offs" ... and you get the idea.
So it has little to do with the rational need your comment implies.
And at the moment there are unpredictable aspects to international cooperation that make it difficult.
Still, I think Obama will bring off some big things this way ... eventually. The timing at this moment doesn't allow it. First the US needs to get its "NASA house" in order - we're a long way from that.
3. No. Realistically, radiation exposure and logistics costs require nuclear.
You can do it with chemical but because you can do something doesn't mean it does get done that way.
I personally don't think there's any serious interest in getting to Mars in a decade unless you have funded, active nuclear exo atmospheric propulsion. -
#153 by mmeijeri on 24 Jun, 2009 06:38
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3. No. Realistically, radiation exposure and logistics costs require nuclear.
Even with things like SEL-2 staging, Earth swingby, reuse of the MTV and use of the interplanetary transport network for cargo and propellant? -
#154 by Archibald on 24 Jun, 2009 16:14
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3. No. Realistically, radiation exposure and logistics costs require nuclear.
Even with things like SEL-2 staging, Earth swingby, reuse of the MTV and use of the interplanetary transport network for cargo and propellant?
Good luck convincing public opinion you want to fly nuclear reactors in space...
(not that I share these fears: Molten Salt Reactors look like a fine concept, sure enough to fly in space)
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#155 by mmeijeri on 24 Jun, 2009 16:46
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Good luck convincing public opinion you want to fly nuclear reactors in space...
Maybe it would be acceptable in sufficiently high orbits. No nukes below GEO sounds like a plausible if arbitrary rule. But the things I mentioned above were proposed by Huntress et al to avoid the use of nukes. -
#156 by nooneofconsequence on 26 Jun, 2009 18:13
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Well, this is one of the reasons we're not going to Mars.
And I suspect we won't until we become more realistic as a culture.
Its not the technology that limits us, or the budget. Its human nature and motivations. -
#157 by Patchouli on 26 Jun, 2009 18:40
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3. No. Realistically, radiation exposure and logistics costs require nuclear.
Even with things like SEL-2 staging, Earth swingby, reuse of the MTV and use of the interplanetary transport network for cargo and propellant?
Good luck convincing public opinion you want to fly nuclear reactors in space...
(not that I share these fears: Molten Salt Reactors look like a fine concept, sure enough to fly in space)
I feel the anti nuclear crowd probably are the biggest obstacle outside of politics and the Earth's gravity well to human space exploration beyond LEO.
It's just such an enabling technology you have to be a complete fool to not take advantage of it.
Some engines such as the molten saltwater rocket have such great performance they make deep space missions almost easy. -
#158 by cgrunska on 05 Aug, 2009 21:13
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So what are nasa's plans on figuring out microgravity effects on biological creatures prior to moon/mars/neo missions, if they threw away the "artificial gravity" maker (centrifugal module)
Wont that want to be known prior to sending dudes up for 3 years? -
#159 by Kaputnik on 06 Aug, 2009 19:52
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I'm not aware of any active attempts to gather this data. ESA and the Russians are performing bed-rest tests.
Since the current baseline is very much Moon-first, it would seem sensible to gather partial-g data there. Remember, we already send people into zero g for six months at a time, so we can surely perform the first lunar missions in confidence.
I'm still wrestling with the basics.
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