Mars launch cycles

radarredux · Aug 17, 2004

I have read that the energy to reach Mars is at a local minimum every 26 months, and this 26-month cycle is imposed on a larger 15-16 year cycle. For example, the 2003 launch window (used for MERs) was at the 15 year low, and energy levels to reach Mars will climb for the next 7 years or so. The next minimum energy launch window is about 2018. Couple of questions: Does anyone have a link to the data showing the energy levels to reach Mars for the different launch windows? Or does anyone have links to the graphs of the data (e.g., the 26 month energy cycle graphed onto the larger 15 year energy cycle)? On a related issue, does anyone have a link to the expected flight time (for robots or manned missions) to Mars for each of these 26-month minimum launch windows? Thanks

mikejz · Aug 17, 2004

I don't have that the information but do know something you might be intrested in. Every 20 years (the next in 2014) is a free return path for Mars where the path will be Earth-Mars-Venus-Earth.

spacester · Aug 17, 2004

mikejz, that is cool, I did not know that. M-E-M-V-E in 2014, very interesting. RadarRedux, that would be great data to have. If you can find it, I'll wager it was posted within the last 2 years, since I searched hi and low. I can calculate all the numbers you could need for any(*) trip to Mars, given the time of flight and a starting date. I can even plan the round trip for you. (*) – except hyperbolic, which is less than about 25 days; also continuous thrust is not yet implemented. What you are asking about is the Hohmann flight time, this is the least energy but lowest energy cost flight, it is a relatively simple calculation. But I developed the software to calculate all the alternatives so I could point out to folks how you can buy shorter trip times with not that much more deltaV. So I hesitate to give you the numbers for Hohmann transfers, but oh what the heck. Just remember that people should get there faster than Hohmann. Hohmann transfers are almost always cited for equivalent circular orbits, but there ain’t no such thing in the real world, er solar system. Mars’ orbit is very eccentric which changes things a whole bunch, for one thing it requires you to find the correct launch window for a given time of flight. Folks should realize Hohmann transfer times vary quite a bit because the actual orbital radius at the time of arrival varies quite a bit. The following copy and paste results are completely corrected for eccentric orbits. I have very, very high confidence they are 100% correct, but they have never been independently verified. I should point out that plane changes are not accounted for – this leads to the implicit assumption that you have to depart Earth at just the right moment. Further, you have to be in the orbital plane around Earth that matches the plane Mars will be on when you arrive. This has significant logistics implications; the trade-offs could lead to a fun discu <div class="Discussion_UserSignature"> </div>

spacester · Aug 17, 2004

Hmm... actually this post is going to be very long. Maybe I should ask if y'all want to see it. Here's a sample, this is the first data set of ten to cover departures until late 2024. ************************* Away transfer insertion date is ........ 2005-AUG-13 03:07:45 Orbital insertion at destination date is 2006-MAY-22 07:03:24 Return transfer insertion date is ...... 2007-AUG-07 08:01:00 Orbital insertion at origin date is .... 2008-APR-05 02:26:54 Wait time prior to away mission is 359.9420 days, Time of flight away mission is 282.1636 days, Hohmann flight Stay time at destination is .... 442.0400 days, 64.3473 % of Martian year Time of flight return mission is 241.7680 days, Hohmann flight Total Mission time is .......... 965.9716 days ***Delta V values corrected for eccentric planetary orbits*** ***Delta V values corrected for parking orbits around planets*** *Parking orbit at origin prior to away trip: Periapse altitude= 375 km, Apoapse altitude= 400 km *Parking orbit at destination after away trip: Periapse altitude= 500 km, Apoapse altitude= 50000 km *Parking orbit at destination prior to return trip: Periapse altitude= 500 km, Apoapse altitude= 600 km *Parking orbit at origin after return trip: Periapse altitude= 475 km, Apoapse altitude= 500 km **Target altitude at destination (impact parameter) = 6507 km **Target altitude at origin (impact parameter) = 24000 km ***Delta V values corrected for gravity losses*** Delta V for gravity losses, start of away mission = 0.1721 km/sec Delta V for gravity losses, end of away mission = 0.1259 km/sec Delta V for gravity losses, start of return mission = 0.2854 km/sec Delta V for gravity losses, end of return mission = 0.2601 km/sec Burn Time, start of away mission = 1800 sec Burn Time, end of away mission = 1800 sec <div class="Discussion_UserSignature"> </div>

mikejz · Aug 17, 2004

I know it is neat! Mainly I think it would mark an intresting oppounity for a minature (possibily university or private) planatary mission--while flyby, its a start. After all, that fact that you are coming back to earth removes the HGA and the need to point the antenna to earth, along with the power requirments. Just store the data onboard and download it at high speed when you come back to earth. I could see one of those cube sats doing it.

spacester · Aug 19, 2004

That's a cool strategy, getting rid of the whole bandwidth apparatus would save a ton of cost. You could even do the "download" via parachute ala Genesis except with a RAM module. A sample return could be done as well. 2014 would be about right. How about a swarm approach - maybe twelve independent return capsules from small lander/samplers sent to the Martian surface. Have half of them bring fuel with them and half demonstrate in-situ propellant synthesis. See how many return, sell half of the returned downmass on the open market, science gets the rest. <div class="Discussion_UserSignature"> </div>

viscor · Sep 15, 2004

Well mikejz your idea with a cubesat or microsatelite is not that bad, which is actually why I am posting. As a member of one of the cubesatprojects (www.cubesat.auc.dk) I would love to see a cubesat fly to mars, and currently my old(I graduated a few weeks ago) university is looking into the posibilities of sending a micro/pico satellite to mars. So to you and all others here, did you ever find out how to calculate a minimum delta v to mars? i need a delta v estimate for launch year 2007 and the needed delta V being from GTO to mars interception. Aerocapture is to be attemptedm so no need to use delta V when arriving to mars. Any good links/programs/estimates would be welcome Viscor

mrmorris · Sep 15, 2004

Minimum deltaV requirements use Hohmann Transfer Orbits -- described in more detail than you would ever ever ever want to know here. However -- such a transfer requires *lots* of time (~19 years), and your cubesat will probably be fried long before reaching Mars. Such a satellite will likely have a much more limited lifetime than a larger one built with multiple redundancies. Since the satellite mass will be low (i.e. more bang for the propellant) -- your better bet is to look for the *fastest* reasonable flightpath rather than one requiring the least deltaV. However -- I have grave doubts about the feasibility of what you suggest, as there are several requirements that scale an interplanetary probe up. - Communication: The cubesat must have a large enough antenna to communicate with earth. It's *conceivable* that you might be able to use 'The Interplanetary Internet' (i.e. messages relayed through NASA/ESA orbiters) to communicate with Earth -- however, you certainly couldn't depend on this for the orbital insertion. - Aerobraking: The cubesat would need an aeroshell for such. More size/space. - Power: While a small panel of solar cells works for cubsats in Earth orbit -- a much larger array is needed for the same rate of power at Mars. This is compounded by the fact that *greater* amounts of power are required at Mars to power communications. - Radiation Shielding: Cubesats in Earth orbit are shielded by the magnetosphere. No such benefit is available in Mars orbit -- or on the way there. More mass to shielding is required and additional hardening of the electronics. I'd think that sending a cubesat to a lunar orbit would be a much more reasonable goal.

viscor · Sep 15, 2004

Thanks for your input mrmorris I probably wasnt clear enough in my first post The actual thoughts are regarding a 100 times larger satellite then the cubesat, ie. around 100 kg in stead of 1 kg. It is one of the aspects of the project to figure out what size could be feasable, if it requires 200 kg, then maybe so be it, if it can be done with 30 kg, great. As to your comment on the hohmann transfer you are absolutely correct we do not have 19 + years to awayt the arival. Realistically maybe one year..maybe two but probably preferably less. As this does not utilize the hohman transfer what other methods would be realistic (within a 3-24 month travel time)? I know how to build the damn thing but must unfortunately admit to a severe lack in orbital dynamics. Viscor

mikejz · Sep 15, 2004

Maybe I could explain what I had envisioned for a mini mars mission… A small satellite would be either launched as a piggyback mission of an existing mars mission or launched to GTO. If it was launched to GTO the satellite would either use a small solid kick stage (spin stabilized) to get to Mars or electric propulsion (probably not ion, but a large arc-jet) to slowly raise the orbit ala Smart-1. Google Amsat P5-a for more info on doing a Mars mission from GTO. Either way to keep costs low, very safe propellants would be used as not to scare the primary customers—I would try and use resistojets, arc jets, or launch with water and use electrolysis to get propellant as needed. Nasa will never let you piggyback a Mars launch if there is anything on your satellite that could remotely compromise the mission…. I was thinking of doing a 2014 launch because of the configuration that you could launch from earth, then do flybys or both Mars and Venus and then return (well not really return, just fly by earth again…). This takes out the issues of communications as it would fly by again and downlink saved data, a low gain antenna would do for basic communications during the mission. Power and radiation: If you store most data onboard and only downlink it to earth on the subsequent flyby you will not need a lot of power for communications. Radiation of course is an issue, however you might be able to kill two birds with one stone by using a lot of batteries to serve as the primary power source during the flybys and arrange them to also shield the sensitive electronics. In closing 1. I would aim more for a flyby than an orbit 2. Look into Amsat P5-a, there is an excellent paper on a mini mars mission 3. Think of maybe a micro atmospheric probe or something like Deep-Space 2.

mrmorris · Sep 15, 2004

"If it was launched to GTO the satellite would either use a small solid kick stage (spin stabilized) to get to Mars or electric propulsion (probably not ion, but a large arc-jet) to slowly raise the orbit ala Smart-1." A solid kick stage gives you one burn. An interplanetary probe will need a propulsion system that can burn on multiple occasions. Electric propulsion of any type requires a *lot* of electricity. This means oversized solar panels. While the panels will assist in the power problem for communications, it is generally not something that is associated with a cubesat. "Google Amsat P5-a for more info on doing a Mars mission from GTO." I found lots of hits, but none with details on how they planned to get the probe there. "...and use resistojets, arc jets, or launch with water and use electrolysis to get propellant as needed." Again -- lots of power required. "Nasa will never let you piggyback a Mars launch if there is anything on your satellite that could remotely compromise the mission…. " If we're assuming NASA lets you in on a Mars launch (unlikely) -- presumably they would take you the whole way there. I doubt they'd take you to orbit, drop the cubesat off, then continue their Mars trajectory. What such a plan would gain in not having to delta-v the mass from earth orbit to Mars, they would have lost (and more) by having to loft the cubesat's engines and propellant from ground to GTO. "I was thinking of doing a 2014 launch because of the configuration that you could launch from earth, then do flybys or both Mars and Venus and then return (well not really return, just fly by earth again…). This takes out the issues of communications as it would fly by again and downlink saved dat

najab · Sep 15, 2004

>So you're proposing a mission that involves a year of flight from Earth to Mars to get a few hours of data (one swipe around the planet) then a year`to get back to download a squirt of info. Then a year to Venus -- a few more hours of data, a year to Earth, another squirt. That's a whole lot of effort for a very little bit of science.First off the trajectory would be Earth-Mars-Venus-Earth. Secondly, the value of this mission wouldn't be the science - at least in my estimation. The real value of the mission would lie in the fact that a planetary mission would be conducted by a non-governmental agency for a tiny fraction of NASA/ESA/JAXA prices. In much the same way that the X-Prize isn't an end but a beginning, this mission would force people to reevaluate attitudes towards the development of space.

mikejz · Sep 15, 2004

A solid kick stage gives you one burn. An interplanetary probe will need a propulsion system that can burn on multiple occasions. I was referring based on the assumption that it was in GTO, after that your propulsion needs are not that large, esp for a low mass probe--look at voyager I found lots of hits, but none with details on how they planned to get the probe there. http://www.amsat-dl.org/p5a/p5a-to-mars.pdf ".Electric propulsion of any type requires a *lot* of electricity. This means oversized solar panels. While the panels will assist in the power problem for communications, it is generally not something that is associated with a cubesat. Or Time, either one will do. After all you could spend days or weeks breaking down water until you need to do a maneuver. Also, Microsat missions have already used resistojets--mostly pulled from batteries. If we're assuming NASA lets you in on a Mars launch (unlikely) -- presumably they would take you the whole way there. I doubt they'd take you to orbit, drop the cubesat off, then continue their Mars trajectory. What such a plan would gain in not having to delta-v the mass from earth orbit to Mars, they would have lost (and more) by having to loft the cubesat's engines and propellant from ground to GTO. That is not what I had in mind. I was referring to the fact that the Delta II kick stage that Nasa uses to get payloads into Interplanetary space contains ballast to stop its rotation (its spin stabilized during the burn) I don't see why that could not be replaced with a microsat. It would get the DeltaV and after that it’s on its own. So you're proposing a mission that involves a year of flight

mrmorris · Sep 16, 2004

"Of course it’s not going to be a 10cm cube, but I could see something under 100 pounds doing the job. I would say that that it would be a cubesat core with the added power and propulsion systems added to it." My original post was in reply to the statement: "...your idea with a cubesat or microsatelite is not that bad..." My entire post was that a cubesat couldn't do it because it needed x, y, and z. Once you add x, y, and z even if the 'core' of the probe is built around a cubesat -- it's no longer a cubesat! Nowhere in there did I claim that it was impossible to make an interplanetary probe that is considerably smaller than those created by NASA. If you can figure out a way to do everything your Mars probe needs to within a 10cm cube, then feel free to argue with my post.

mikejz · Sep 16, 2004

Cube, Micro, Mini, Picosats---I always get them mixed up<img src="/images/icons/smile.gif" /> Bottem line, I was talking about a small mission on the 50 pound range.... Never said it had to be exclusitvely a cubesat Anysays, could a cube sat do a interplanetary probe be done? It could if laser communcations made communications a small mass factor.

mrmorris · Sep 16, 2004

"Almost all cubesat programs I have read about are more about engineering than science--it’s not about new planetary science, its demonstrating that a small group could design the flight hardware to do it on a small budget. " Agreed. Currently -- a large number of cubesats are little more than modern day Sputniks... orbiting boxes that go 'ping'... and not much else. However -- it is very easy to see how they will be capable of a great deal more in the near future. As cubesat engineering matures in the next 10-15 years, they will begin to have capabilities generally associated with much larger satellites. Because they use OTS components -- relative computing capacities will increase much faster than their larger cousins. Because they are so much smaller than conventional satellites, power and stationkeeping propulsion requirements are significantly reduced. Cubesats in earth orbit have obvious near-term potential. By contrast -- an interplanetary mission such as you describe offers little more than a 'first'. Firsts are nice, but it's better to accomplish something with lasting value. Jump forward a decade or so when cubesats are both more common and more capable. I could see it as being a worthwhile mission for NASA to develop a Mars 'Cubesat Carrier' (we can it Nimitz). The carrier itself would be little more than a framework to carry lots (10, 20, 50?) of cubesats, a large antenna and solar array, and propulsion capabilities to allow significant maneuvering once in Martian orbit. On arriving at Mars, it would 'seed' the cubesats into various orbits around Mars, and would itself act as a communications relay to stream their data back to Earth. Such a plan would make full use of the potential of cubesats. The power and propulsion issues would be negated by the carrier concept. It would also eliminate a significant problem I didn't mention (but the P5A paper did) -- namel

mikejz · Sep 16, 2004

I like the idea Of course that does not take away the value of firsts. Afterall, a lot can be gained in terms of making systems smaller, and by showing that it can be done will make funding more missions of your type a lot easier. Far out idea: Why not make a small fleet of Microsats that would make there way out to Saturn and take dives into Saturn’s rings while using Cassini (which would be ending its useful life) as data rely.

mrmorris · Sep 16, 2004

"a lot can be gained in terms of making systems smaller, and by showing that it can be done will make funding more missions of your type a lot easier. " Most of the improvements that can be made in such a mission involve creating a cubesat with more capability for a given mass. That type of development is better done in LEO, where the number of risks *unassociated* with the cubesat capabilities itself are minimized. After all -- it matters not how capable the cubesat probe itself is if the drive fails somewhere between Earth and Mars. The *hardest* part of missions to Mars is getting there. Once cubesats with truly impressive capability-to-mass ratios exist, then getting funding for CS missions becomes much more likely. Re: Saturn -- just a bit too far out for the idea. Solar is impractical at that distance and RTGs ain't workable for cubesats.

mikejz · Sep 16, 2004

The biggest challenges to a Interplanetary mission with cube sats is three fold. None of these are like the conditions in LEO. 1. Radiation 2. Attitude control (most cube sats rely on earth's magnetic field to do this) 3. Communications While Microsat Mars missions sound nice, I really seem them exploring asteroids. After all, even a flyby mission would return significatly more science on most objects than we currently have. They are also cheap, and you could launch many to scout out possible canidates for more tradition probes. The Saturn idea is way out there, however given that the goal is simply to crash them into the rings, the actual mission would have the same length as the Huygens probe--which runs on just batteries. Of course getting there is another question...but I did say it was a far out idea.

backspace · Sep 16, 2004

I read the Amsat document... One thing though, this doesn't sound right to me.. I can't put my finger on it but the mechanics of this seem wrong: "With a closer examination it turns out that the law of energy conservation of physics comes to our aid: if one accelerates the satellite at perigee, only about 1 km/s is needed to leave the earth‘s orbit and to •take along" about 3 km/s. This is the result of the high velocity at perigee and of the fact that the energy is a square function of the velocity."

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