Abort options on a interplanetary mission

[willpittenger]

Apollo missions included an abort option called a free return. The TLI burn left the craft on a trajectory that unless changed would send it back to the earth rather than lunar orbit. However, what about a trip to Venus, Mars, or an asteroid? Such trips would leave the Earth's gravitational influence so I doubt a free return would be an option. <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[kelvinzero]

I was wondering about this too.<br /><br />Can you gain a boost by slingshotting around the moon?<br />If so, could you do your entire burn for mars before reaching the moon, and simply slingshot home if your main engine fails?

 

[holmec]

<blockquote><font class="small">In reply to:</font><hr /><p>Can you gain a boost by slingshotting around the moon?<p><hr /></p></p></blockquote><br /><br />I would have to guess that sling shotting around the moon would gain you speed which you don't want. To return to earth from the moon or a high Earth orbit (as the moon is) you would need less velocity.<br /><br /> <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[holmec]

<blockquote><font class="small">In reply to:</font><hr /><p>However having that capability with today's technology level is not practical due to the extra mass of propellant that would be needed.<p><hr /></p></p></blockquote><br /><br />I would imagine that by the time the vessel is on its way to the target planet, that most systems would be stable. And that most abort scenarios at that point would be medical or crew related.<br /><br />But if the service module of the Orion would die on the way to, say, Mars, I would assume that there would be enough fuel to:<br /><br />1. make a alternate trajectory for a high earth orbit to loop back. (Shuttle_Guy says "not enough fuel")<br />or <br />2. have enough fuel to loop around Mars rather than orbit it.<br /><br />Now my question is this: Does it take more fuel to set an orbit around Mars or to loop around it and return to Earth? <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[MeteorWayne]

Depends on which way you go. You can gain or lose energy. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[itsfullofstars]

As far as I understand it, you reach the point of no return after about 2 weeks. Before the two weeks you can use the free return. This is assuming we are using the conjunction mission plan, where the craft sets off as mars is approaching it's closest distance from earth.<br /><br />After the point of no return the only way home is to continue to Mars and land, or stay in orbit, for over a year until earth and mars were in the right places again. <br /><br />itsfullofstars

 

[henryhallam]

<font color="yellow">(Shuttle_Guy says "not enough fuel") </font><br />Ooh, he'll have your guts for garters!<br /><br />I don't think the standard 6-month Mars trajectory has any slingshot return options available. There was talk about a longer trajectory that went via Venus on either the outbound or return leg, and IIRC that one had a free-return capability without needing a large burn at either planet. Unfortunately it takes much longer, so unlike Apollo where the free-return brings you home in three days, this would take more than a year.<br /><br />See this also: http://cat.inist.fr/?aModele=afficheN&cpsidt=13500027 though you need an AIAA subscription to read it and it is talking about a 2014 mission which might be a bit optimistic.

 

[vogon13]

The Orion Nuclear Impulse craft from the sixties could turn around and come back at any point in the flight path.<br /><br />{not that you might want it to return to earth . . . .}<br /><br /><br /><br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[willpittenger]

There is a miscommunication somewhere. The definition of a free return that I know off is that you can make the trip back without burning any fuel. So how your free return work? <div class="Discussion_UserSignature"> <hr style="margin-top:0.5em;margin-bottom:0.5em" />Will Pittenger<hr style="margin-top:0.5em;margin-bottom:0.5em" />Add this user box to your Wikipedia User Page to show your support for the SDC forums: <div style="margin-left:1em">{{User:Will Pittenger/User Boxes/Space.com Account}}</div> </div>

 

[kelvinzero]

me: <font color="yellow">I was wondering about this too. <br /><br />Can you gain a boost by slingshotting around the moon? <br />If so, could you do your entire burn for mars before reaching the moon, and simply slingshot home if your main engine fails? </font><br /><br />Hi again,<br />I dont think I asked that very well. I was really asking two questions. The first question should actually have been <font color="yellow">Can you gain a boost by slingshotting around the moon <i>for your trip to Mars?</i></font> Im guessing you gain about 1 km/s doing this. On the other hand I can't find a reference to it so maybe Im wrong.<br /><br />If a moon slingshot is generally useful that could open up a possibility to return home. Suppose your main engine fails half way through it's burn. You might be unable to directly return to the earth, but also unable to make it to mars where perhaps a backup craft awaits you.<br /><br />But in this case, since you are already aimed at the moon, couldnt you use smaller rockets that may not have failed to adjust your trajectory to make a 180 degree slingshot around the moon, instead of a 90 degree one towards mars, and return home? Although you dont have fuel or an engine to stop, you can use earth's atmosphere to capture you.<br /><br />That was my idea anyway.

 

[qso1]

For my graphic novel, I actually used Starry Night to look at abort option scenarios. I didn't spend a lot of time on it but I did see why some scenarios are simply not possible. One of which was simply looping back. Looping back without propellant meant looping back to where one might like the earth to be but it isn't because of the difference in orbits.<br /><br />Of course, this is just a graphic novel and my main purpose was to show what is meant by aborting from a planetary trajectory and to hopefully show what I think it actually looks like graphically. It also depends on what kind of craft (Chem, NTR, Nuke-elec)is going to get you to mars. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[qso1]

It can probably be done but only in the rarest of scenarios. The Earth Orbit Departure (EOD) geometry would have to be planned to take this into account. This idea would have to be studied a bit further to see if its practical or even possible.<br /><br />For one thing, we need to know some particulars about mission/spacecraft/trajectory design to see what may or may not be possible. What may be impossible for a chemically propelled mars craft may be within reach of an NTR or nuclear electric powered craft.<br /><br />If a mars mission were being developed at this time...we'd most likely go with the least expensive option which in this case would probably be chemically propelled.<br /><br />I hate to say it but I think given the reality of space budgets, public and political will....if or when we finally send humans to mars and barring some major techno-economical paradigm shift. We may have to live with the reality of a mars mission or missions in which there are no abort scenario possibilities just as we now live with it on the first two minutes of shuttle launches in which an SRB failure would likely prove catastophic as one did on Challenger. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[qso1]

willpittenger:<br />The definition of a free return that I know off is that you can make the trip back without burning any fuel. So how your free return work? <br /><br />Me:<br />Good point, and not only that, will earth be in the correct position to return to for a craft returning with no propellant? <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[holmec]

good point. <div class="Discussion_UserSignature"> <p> </p><p><font color="#0000ff"><em>"SCE to AUX" - John Aaron, curiosity pays off</em></font></p> </div>

 

[henryhallam]

It is worth noting that only the first couple of Apollo missions had true free-return trajectories. The later ones, including 13, required fairly significant adjustments to go back to a free-return profile after TLI. But these adjustments could be made using just the RCS thrusters, and if you'd lost those then you were in real trouble.

 

[itsfullofstars]

Sorry yes I shouldn’t have used the term free return in my last post as it would not be a true free return, you have to burn propellant in the scenario I was talking about.

 

[mithridates]

Looking at this thread makes me wonder if it might be worth it to set up a permanent unmanned waystation trailing Mars' orbit near a trajectory we'd have to make to get to Mars, just in case something goes wrong on the way. Say if something happened like in Apollo 13 with oxygen and the crew had enough time to get somewhere but not back home, at the least they could make their way to the waystation and camp out there where they would either be able to fix the problem with extra supplies and then go on to Mars, or wait until Earth nears again and they're able to go back.<br /><br />Does that sound at all realistic? <div class="Discussion_UserSignature"> <p>----- </p><p>http://mithridates.blogspot.com</p> </div>

 

[samkent]

All future craft would have to be use the same equipment to dock with the emergency supply craft. That limits future designs.<br /><br />Critical failures on the Mars bound craft would leave little time for self rescue.<br /> <br />Air leak? Dead in hours to days.<br /><br />Part failure? I doubt current repair parts would be of any use to future craft. Besides that one part you need would be the one they didn’t stock.<br /><br />Engine failure? Inability to rendezvous with emergence craft.<br /><br />Spoiled food? 6 months is a long time to go without food.<br /><br />Medical problems? Maybe an additional supply of certain drugs would be helpful assuming the crewman didn’t die in the first several months after the problem came up.<br /><br />Nope it would be a big waste of money.<br />

 

[lampblack]

Or... perhaps Mars missions could be designed such that manned spacecraft are launched in pairs.<br /><br />If there are two ships flying the same trajectory, one could be used as a lifeboat if something went haywire on the other. <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

 

[earth_bound_misfit]

"2. have enough fuel to loop around Mars rather than orbit it. "<br /><br />You just one of SG's pet peeves.<br />Another is the Orbiter/ Shuttle/STS thing <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p> </p><p> </p><p>----------------------------------------------------------------- </p><p>Wanna see this site looking like the old SDC uplink?</p><p>Go here to see how: <strong>SDC Eye saver </strong>  </p> </div>

 

[scottb50]

First the orbital geometry between Mars and Earth is constantly changing, second the way you get to either is by entering an orbit around the Sun that intersects the planetary orbit. If you loop around Mars you could intersect Earths orbit but where Earth would be at that time would be the big question. <br /><br />Your waystation would present another problem in that it would take a lot of energy to rendezvous with it and would not have gravity of the planet to assist in reaching an orbit. <div class="Discussion_UserSignature"> </div>

 

[qso1]

This was one of the ideas behind the old Von braun mission plans. Two ships with 6 or 12 men each would go to mars and one would serve as backup if the other had to be abandoned. I don't recall if aborts involving returns to earth were covered.<br /><br />The reason this wasn't present in mars concepts after the 1960s...the cost barrier. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[qso1]

The problem is trajectory to mars varies with each mars mission opportunity. A mission that may be planned for a 2020 launch is scrubbed due to some major problem preventing EOD. The 2020 window runs out. Next attempt, 26 months later or 2024. The trajectory for 2024 runs similar to 2020 but offset due to planetary positions, particularly mars. I actually verified this in Starry Night. A way station positioned for a 2020 mission would need significant propellants to position for a 2024 opportunity.<br /><br />The added cost of a way station will cause it to be cut under current and projected political/budget realities IMO. Technically realistic to some degree but financially, not realistic under present/projectable conditions.<br /><br />Scottb50 explained the orbital mechanics of the situation pretty well. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[R1]

The crew would be the most important, so the ships carrying the crews will<br />probably be relatively smaller and thus more economical to mass produce. This would<br />make it easier to send crew ships in pairs.<br /><br />I had an idea on another thread somewhere of moving a small asteroid closer to us than Mars,<br />a small one, like Ida's moon Dactyl or even smaller, where fuel, oxygen, and vital emrgency components could be stored<br />for a similar purpose as a midway station. But I'm not sure how complicated this would be, does it sound<br />realistic to do this? My fear is that too much fuel would be required, but I have read somewhere else<br />about ideas of moving asteroids with the mere gravity from a nearby ship. Granted, this idea was to <br />barely budge an asteroid out of a dangerous trajectory, but even with a small amount of fuel, my thought is that<br />a small asteroid could be brought in closer than Mars, and thereafter, <br />(once it is closer to earth) it would be much easier to both refuel<br />its movement rockets and supply it adequately. <div class="Discussion_UserSignature"> </div>

 

[MeteorWayne]

Whether moving an asteroid with a rocket or mass driver on the surface, or using a gravity tug, the same amount of fuel is required, because the same mass (the asteroid) would be moved to the same orbit, requoring the same energy. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>