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#76 Re: Mars Society International » Zubrin blasts Obama » 2011-11-27 20:12:44
There are, however, some of his programs which I simply find it quite difficult to care about. The new HLV, for example, is in my opinion farcial and is probably never going to get built.
The SLS isn't Obama's program.
Fortunately, the programs to make it possible for private companies to develop space transportation systems have been kept operational and these are in my opinion the most important things that NASA can be doing right now.
Commercial has been slashed to half of what Obama asked for -- to 400 million. The SLS has been increased to 1.86 billion. A defeat for Obama but a victory for some Republican senators whose districts will benefit from SLS.
#77 Re: Mars Society International » Zubrin blasts Obama » 2011-11-27 20:06:05
Like with so many things, there is a grain of truth and point to be made here. NASA's planetary science program has recently pushed through most of the big ideas in the pipeline (MESSENGER, New Horizons, Dawn, Juno, MSL, MAVEN, etc.). After this, future missions are shamefully ill defined. This is largely due to NASA's general near term financial uncertainty. It is even having trouble meeting obligations for planned near future missions for which hardware is ready to be built (like the Mars Trace Gas Orbiter jointly administered with ESA). There is no plan for exploring Mars in the 2020s. You will hear talk about a sample return, but there is no real, cogent plan. And then you have murmurings of a manned mission in the 2030s. There are a lot of planetary science missions to be done before that! The situation is similar with regard to the idea of an orbiter for Uranus, a robotic probe to penetrate Europa's subsurface ocean, and various other things on the planetary science community's "wishlist".
Oh, there's no doubt support's lukewarm and that planetary exploration is underfunded.
Here is a video of subcommittee hearing on planetary science. Green and Squyres complain of the OMB's unwillingness to commit to ambitious joint NASA-ESA Mars missions. Dr. Green says (name mumbled) told him OMB wouldn't commit to Mars 2016 and 2018 (at 36:00 minutes into the video). I suspect Green's conversation with this person from the OMB is the source of Zubrin's "word has leaked out."
OMB's unwillingness to commit to Mars Missions is not remotely the same as "terminating NASA's planetary exploration program".
Distressing as this is, to say that the planetary science program is going to be terminated is completely inaccurate.
That is my opinion. I suspect Zubrin was exaggerating for dramatic effect. If so, he will get a reputation for crying "wolf".
#78 Mars Society International » Zubrin blasts Obama » 2011-11-27 16:06:06
- Hop
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According to Zubrin, the Obama administration intends to terminate NASA's planetary exploration program.
Extraordinary claims require extraordinary evidence. But Zubrin names no source. "Word has leaked out" is the foundation of his claim. In my eyes, this lessens Zubrin's credibility.
#79 Re: Terraformation » Creating a (small) Lunar atmosphere » 2011-11-27 15:41:24
I'm talking about an atmosphere of ~5mb - Areoforming, if you like, rather than Terraforming. This would result in cloud cover over the moon, hopefully an Ozone layer forming, a smoothing out of temperature, and allow small craft to aerocapture.
Since the lunar surface is vacuum, you can launch via rail. Not only does this eliminate gravity loss, but also allows you to cut some km/s from your delta V budget when figuring reaction mass. An atmosphere could take that away. An atmosphere would be a net loss in terms of delta V, in my opinion.
The best place to settle is near the volatile deposits in the lunar cold traps. Plateaus neighboring some of these cold traps enjoy nearly perpetual sunlight. The temperature swings for these is plus or minus 10 degrees.
The habs would still need radiation shielding, even with a 5 milli bar atmosphere
#80 Re: Meta New Mars » Newmars Users » 2011-11-23 14:26:16
Wonderful. Hoping this forum thrives in its second incarnation.
#81 Re: Water on Mars » MARSIS is ready to work! » 2005-06-26 16:14:36
http://spacenews.dancebeat.info/article … ork]MARSIS ready to work!]MARSIS read to work!
Subsurface liquid water is one of the things they'll search for with MARSIS' deep penetrating radar.
#82 Re: Unmanned probes » MARSIS ready to work! » 2005-06-26 16:03:18
http://spacenews.dancebeat.info/article … ork]MARSIS ready to work!
MARSIS is part of ESA's Mars Express. It uses radar to probe Mars surface up to 5 kilometers deep. One of the things they hope to find is subsurface liquid water.
#83 Re: Civilization and Culture » Sun-Mars L-4 and L-5 » 2005-05-31 07:43:53
The Earth Sun L4 and L5 would be better places for communication relayers. The path is shorter by .52 AU. Interestingly enough the long legs for both these paths is the same: 2.2 AU. But the short legs differ, earth's being 1 AU and Mars being 1.52 AU.
The earth L4 relay could get double the solar energy with the same collector and is closer to Earth.
The only advantage I see for the Mars L4 is the Mars Trojan asteroids RobS mentioned.
#84 Re: Interplanetary transportation » Interplanetary supply infrastructure - Cyclers vs. one way capsules » 2005-05-13 18:09:24
Just looked up the chapter about solar sails of another space book. Looks like I was wrong with that guess before. As I reflect on it the fact that the resulting impulse vektor depends on the angle by which the stream is diverted is an indication of it being possible to deccelerate.
They give a system of differential equations to calculate the orbital motion of the sail. Since I'm not quite up to solve them at the moment, I'll just believe that the articles are right and I'm wrong
Sounds like an interesting book. Could you give name and author or maybe an Amazon link?
#85 Re: Water on Mars » Marsis to probe for subsurface water » 2005-05-06 12:39:57
Much about this radar has been mentioned under the Mars express thread but ok it would seem that the first boom is out to be followed by others. Not to mention it did not kill itself from whipping as the simulator had indicated.
http://www.msnbc.msn.com/id/7751425/] Radar readied to search for Martian water;
Mars Express orbiter reportedly releases first boom
(looking in the Unmanned Probes topic...) I see your April 29 post but don't have time right now to read the entire 10 page thread.
The Marsis antenna is only 1.8 kilograms. Seems like it'd be worthwhile to use something like it to probe the moon. Or asteroids & comets for that matter. We'll have to wait and see if it unfolds without a hitch.
The Oberg article is good. Thanks for the link.
#86 Re: Water on Mars » Marsis to probe for subsurface water » 2005-05-05 13:38:51
http://mars.jpl.nasa.gov/express/spotli … 50504.html
This is very exciting to me. There is little doubt that there is frozen water on Mars. But permafrost is a difficult rock to work with.
There's some evidence of Martian volcanic activity in the recent (geologically speaking) past. I believe it likely there is liquid water near the surface of Mars.
If the Marsis antenna does find near surface liquid water, this will be very valuable information.
#87 Re: Interplanetary transportation » Earth Mars delta vees » 2005-04-16 14:01:34
The first seven cells of row 12 is the starting point info and the first seven cells of row 13 is destination info.
So to start from Mars copy the 7 martian cells closest to the departure date and paste them into the 12th row.
Then find the 7 earth cells closest to arrival date and paste them into the 13th row.
It's aggravating that it runs iterations each time data's changed. But it goes through them faster if the reset cell (B7) equals zero. Then when all the info is entered, set the reset to equal 1.
I believe 100 iterations is Excel's default. But 50 probably suffices.
#88 Re: Interplanetary transportation » Earth Mars delta vees » 2005-04-14 12:16:30
I recently made a spreadsheet for non-Hohmann Earth Mars (or vice versa) trips. I've been wanting to do this for a long time. RobS provided the nudge.
Years and AU (astronomical unit) are the preferred units. Traditional dates are an unwieldy combination of years, months and days. I use
http://clowder.net/hop/date]http://clow … alyear.xls
to convert dates to decimal years.
Once a date's in decimal year format, Earth or Mars coordinates close to that date can be found in
http://clowder.net/hop/EarthMars.xls]ht … thMars.xls
This gives space time coordinates for each vertice of 1000 sided polygons approximating Earth and Mars orbits.
Also given is velocity vector at a space time point.
This spreadsheet is big - about a megabyte.
The last spreadsheet is
http://clowder.net/hop/lambtrans2.xls]h … trans2.xls
In Excel Preferences iteration must be turned on or Circular Reference errors occur.
Cell B7 is the reset switch. Typing 0 into b7 will erase info stored in iteration cells, typing 1 will restart iterations.
From EarthMars.xls copy space-time coordinates of departure point as well as velocity vector and paste these 7 values into cells A12 to G12 (not an ordinary paste, use Paste Special and choose Value button in dialogue box)
Likewise paste destination coordinates and velocity vector into cells A13 to G13 of the lambtrans spreadsheet.
Hope these are helpful. If anyone finds misteaks or bugs please let me know.
#89 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-10 17:59:42
It depends on what the incoming cargo is. If it is a solid nickel iron shipment, maybe that's too high. If it's a loose, and airy it might be low. I believe we've already deorbited some structures larger than 50 meters, but they were hollow.
Tunguska was thought to be about 100 meters across.
If it's something that will burn up easily, the ceiling could be higher.
We've already practiced aerobraking in the earth's atmosphere with the Challengers. & we've used Mars' atmosphere to slow some of the spacecraft we've sent there. It is still a good idea to practice more aerobraking with Mars and Venus, maybe Titan.
The perigee of the ellipse needs to be above the atmosphere or it'll crash and burn after a few passes through earth's atmosphere at perigee. If aerobraking is used to capture an incoming load, another burn should be done at apogee to lift the perigee out of the atmosphere.
Whether or not all HEEOs are unstable to the point of requiring prohibitive delta vee station keeping expense is something I still don't know.
#90 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-09 13:21:43
Edit #2 - - Use an equatorial HEEO (close to zero inclination) that will assure the northern hemisphere nations (USA, Russia etc. . ) that there is no danger of a large NEO smashing into a city.
Some argue an increased awareness of NEOs combined with space travel abilities would drasticly reduce the chances of Chicxulub or even Tunguska class impacts.
This would be the case if humans were sane. But, IMO, exactly the opposite is true.
Here's a scenario: Al Queda Space Enterprises Ltd. is contracted to capture a nickel-iron NEO to Earth orbit. The accepted plan is to have a very near earth perigee to exploit aerobraking and the Oberth effect to shed velocity. But at the last minute the trajectory is somehow off by a fraction of a degree and aerobraking becomes lithobraking.
I advocate ceilings on the sizes of imports to near Earth space.
#91 Re: Interplanetary transportation » Mars Dogleg - Phobos refueling station » 2005-04-09 12:50:34
If chord c is long and time short, you need to haul ass to get from point A to B. If you have to go too fast (solar escape velocity or higher), the transfer orbit is no longer an ellipse, but a parabola or hyperbolic orbit about the sun. These solutions lie outside of Lambert's approach.
#92 Re: Interplanetary transportation » Mars Dogleg - Phobos refueling station » 2005-04-09 12:38:11
The sun, earth at departure, and Mars at destination form 3 corners of a Lambert triangle. r1 is vector from sun to departure position, r2 vector from sun to destination position and c is chord from r1 to r2.
Green ellipse is transfer orbit with axis indicated by a green horizontal line.
Notice how Earth and Mars are both on the same side of the axis (the top half?) This is how my Lambert spreadsheet is set up and I'm guessing also Mars Academy's applet.
With a Hohmann orbit departure earth and destination mars are separated by 180 degrees. That puts the departure and destination points right on the boundary -- another degree and they'd be on opposite sides of the transfer ellipse's axis.
I tested this. Using my spreadsheet based on circular orbits I get a Hohmann launch window of May 19, 2003 with about a 258 day trip time. I input this info into their applet - no solution. Then I changed trip time to 254 days and their picture shows a very Hohmann like orbit.
Which leads me to believe that their applet, like my lambert spreadsheet, isn't set up to handle departure and destination points on opposite sides of transfer ellipse's axis.
#93 Re: Interplanetary transportation » Mars Dogleg - Phobos refueling station » 2005-04-08 18:32:53
Here's some studies of the Lambert space triangle:
http://clowder.net/hop/lambert/Lambert. … mbert.html
http://clowder.net/hop/lambert2/lambert … bert2.html
http://clowder.net/hop/lambert3/lambert … bert3.html
Given departure and destination points, a focus, there are usually two ellipses with semimajor axis a that pass through both points. (although sometimes there's just one ellipse and sometimes none. The Lambert.html illustrates those possibilities)
At the bottom of the lambert3.html are 4 possible paths from departure to destination points if your ellipse has a specific semi-major axis. Each path takes a different time. I've been using the top possibility: the path is the short part of an ellipse's circumference where both starting and ending points are on the same side of ellipse's axis.
#94 Re: Interplanetary transportation » Mars Dogleg - Phobos refueling station » 2005-04-08 18:00:19
The 3.94 is leaving transfer for Mars. Mars gravity isn't considered.
3.94 km/sec is Vinfinity of a hyperbolic trajectory. Let's say you set this hyperbola's periapsis at 300 km above Mars surface. Then the hyperbola's periapsis velocity will be 6.22 km/sec.
A 1.74 burn at this periapsis would be enough for capture to an elliptical orbit with a 20062 km apoapsis (Deimos altitude). Then at Deimos a 1.28 burn would match velocities with the moon.
So two burns totalling 3.02 km/sec would land you on Deimos.
#95 Re: Interplanetary transportation » Mars Dogleg - Phobos refueling station » 2005-04-08 16:08:52
Thank you again for your time and effort. The data are not encouraging, that's for sure. If you are in the mood, calculate this one, if you can:
trans-Earth injection from Mars: Oct. 15, 2015
Earth arrival: 15 Mar. 2016 (151 days in transit)
trans-Mars injection: 1 April 2016
Mars arrival: 1 Oct. 2016 (183 days in transit)
This leaves Mars earlier, leaves Earth earlier, spends alonger time in transit, and reduces the time at Earth rather severely.
-- RobS
The first one I'm having problems with. I believe the starting and ending position vectors will be on opposite sides of the transfer ellipse's axis. Will have to study that some more.
The second scenario:
trans-Mars injection: 1 April 2016
Mars arrival: 1 Oct. 2016 (183 days in transit)
is more Hohmann like. 1st delta vee is 5.12 km/sec and the second burn is 3.94 km/sec. Not bad!
I've been wanting to make this spreadsheet for a long time. Thanks for providing a nudge. If I can perfect this, it will be a very useful implement in my tool belt.
#96 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-05 18:52:02
Suppose we move a nickel iron asteroid into a HEEO.
Deploy tethers to accelerate crew taxis and cargo to the HEEO and simultaneously deccelerate the Ni-Fe NEO to a lower orbit for easier mining and delivery to Earth.
If the Ni-Fe is headed for Earth anyway, so what if you subtract momentum from the NEO?
= = =
There is a whole Sci-Fi universe here, with the value of a Ni-Fe NEO augmented by its ability to transfer momentum to spacecraft in LEO, before slowed to a lower orbit and mined into oblivion. Then move a new Ni-Fe NEO into a HEEO.
Buy and sell momentum rights on the commodities market.
If we moved a nickel iron asteroid into HEEO, I'd leave most of in HEEO. It'd be used to make the crew taxi that ferries crew from Low Earth Orbit to High orbital colonies like L4, L5 (and back again). The chief virtue of this metal, in my opinion, is that it's high on the slopes of Earth's gravity well, you don't have to pay a fortune to haul this up from earth's surface.
Same for volatiles mined from asteroids, sent to near earth space and caught in HEEO. Leave it in HEEO.
When it comes time to leave for Mars or elsewhere, send a crewed vehicle from the HEEO facility at perigee. All the fuel, metal, water, etc. in the vehicle would already have most the momentum it needs and a little kick from a tether would send it on it's way.
This would shed some of the HEEO ferry's momentum bringing down it's apogee. But you could compensate by tossing mass in the opposite direction to slow it down to a low earth orbit. There will be folks wanting to return to Earth as well as leave for Mars.
#97 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-05 15:39:04
Aren't highly elliptical orbits also known as high energy orbits? Or did I pick that up wrong, somewhere?
Zubrin writes about a manuever known as the perigee kick with the orbit becoming more and more elliptical after every burn.
Orbital energy is -Gm/2a
G is gravitational constant
m mass of central body
2a is the major axis of the ellipse.
So you see energy relies on length of ellipse and not it's shape. A circle orbit having radius a would have the same energy as a skinny ellipse having semi major axis a. It doesn't depend on eccentricity.
If you want to raise the apogee of an elliptical orbit, perigee burns are the best way to do it.
However if HEEO (highly elliptical Earth Orbit) ferries are possible, I don't propose they be built from Earth materials. Mined Asteroidal resources coming in on a hyperbolic trajectory with a near earth periapsis could be captured with very little delta vee to a HEEO.
#98 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-04 17:45:05
Googling . . . huge pile of irrelevant stuff. Hmmm some interesting biographies of Hermann Oberth, rocketry pioneer . . . dammit.
Well I'll try to describe it. You get more bang for your buck if do your burn deep in a gravity well. Burns at periapsis are recommended.
Without earth's gravity, 3 km/sec a second is needed to leave for Mars from earth orbit. This 3 km/sec is called Vinfinity.
But 3 km/sec isn't your burn if you're leaving from Earth's gravity well. The burn is sqrt(Vinfinity^2 + Vescape^2) .
Concrete examples:
A burn for mars from LEO 300 km up:
Escape velocity's about 10.9 km/sec.
sqrt(3^2 + 10.9^2) = sqrt(9+118.8)=sqrt(130)=11.3 km/sec
Only .4 km/sec is needed in addition to escape velocity
A burn for Mars from GEO 36000 km up:
Escape velocity's about 4.3 km/sec
sqrt(3^2 + 4.3^2) = sqrt(9 + 18.5) = 5.2 km/sec
.9 km/sec is needed in addition to escape velocity.
A burn from 1 Lunar Distance, about 380,000 km
Escape is about 1.4 km sec
sqrt(9+1.96)=3.3 km/sec
Which is 1.9 km/sec past escape velocity.
If your apogee is really high and perigee very low, you'll be going almost escape velocity at perigee. For example the moon resonant orbit I was talking about with LEO perigee and apogee almost as high as the moon is moving 10.8 km/sec at perigee. Add .1 km/sec to get to 10.9 km/sec escape velocity and then with another .4 km/sec and you're on your way to Mars with a .5 km/sec burn.
#99 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-04 13:26:20
Don't need an eternal orbit. An orbit with high apogee and low perigee that doesn't require a lot of delta vee to correct for perturbations would fill the bill.
#100 Re: Interplanetary transportation » Moon resonant orbits » 2005-04-04 10:30:06
Mars has Trojans
http://www.aas.org/publications/baas/v3 … 004/65.htm
The L points are the best known stable orbits but there are others. I've already given examples.
Although the L point orbits need little or no station keeping, they do not suit my purposes. To exploit the Oberth effect for delta v savings, the orbit should be fairly eccentric with perigee deep in Earth's gravity well.