Hohmann Transfer to Mars Reference Thread

[spacester]

Over on this thread, I threatened to post a bunch of data, even though all RadarRedux wanted was a link. It turned out that I had the time available to summarize the results and finish explaining the nuances behind the numbers. So I decided to start this reference thread.<br /><br />I'll skip ahead to the results:<br /><br />DeltaV for Hohmann transfer, km/second<br />From LEO (375 km x 400 km)<br />to HEMO (500 km x 50000 km Martian orbit)<br />Uncorrected for gravity losses:<br />Year. . . . . .Burn1. . . . . .Burn2<br />2005. . . . . .3.7193 . . . . . . 0.5728<br />2007. . . . . .3.7035 . . . . . . 0.6150<br />2009. . . . . .3.6341. . . . . . 0.9179 <br />2011. . . . . .3.5364. . . . . . 1.2450<br />2013. . . . . .3.4338. . . . . . 1.4017<br />2016. . . . . .3.3692. . . . . . 1.2708<br />2018. . . . . .3.5122. . . . . . 1.2991<br />2020. . . . . .3.6989. . . . . . 0.6929 <br />2022. . . . . .3.7181. . . . . . 0.5531<br />2024. . . . . .3.6659. . . . . . 0.7840<br /><br />DeltaV for Hohmann transfer, km/second<br />From LEO (375 km x 400 km)<br />to HEMO (500 km x 50000 km Martian orbit)<br />Corrected for gravity losses (burn time = 1800 seconds):<br />Year. . . . . .Burn1. . . . . .Burn2<br />2005. . . . . .3.8915 . . . . . . 0.6987<br />2007. . . . . .3.9580 . . . . . . 0.7793<br />2009. . . . . .3.8905. . . . . . 1.2923<br />2011. . . . . .3.7285. . . . . . 1.7178<br />2013. . . . . .3.4911. . . . . . 1.8275<br />2016. . . . . .3.5233. . . . . . 1.4142<br />2018. . . . . .3.7039. . . . . . 1.7556<br />2020. . . . . .3.8077. . . . . . 0.9578 <br />2022. . . . . .3.9516. . . . . . 0.6108<br />2024. . . . . .3.9298. . . . . . 1.0880<br /> <div class="Discussion_UserSignature"> </div>

 

[spacester]

What RadarRedux was asking about is the Hohmann flight time, this is the longest trip time but lowest energy cost flight, it is a relatively simple calculation.<br /><br />Having developed the software to calculate all the alternatives, I would like to point out to folks how <b>you can buy shorter trip times with not that much more deltaV</b>. So I hesitate to give you the numbers for Hohmann transfers, but oh what the heck. Just <b>remember that people should get there faster than Hohmann.</b> <img src="/images/icons/laugh.gif" /><br /><br />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 that you 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.<br /><br />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. (Nor have any past postings been refuted <img src="/images/icons/laugh.gif" /> ) I have that same high confidence in any of these results I post, subject to the provisos that follow.<br /><br />I'll be happy to run other calcs on request, just give me the Time of Flight in Earth days and the earliest possible departure date, and I can schedule you for the next flight to Mars and tell you the deltaV requirement.<br /><br />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 discussion: do you use more deltaV to simplify the <div class="Discussion_UserSignature"> </div>

 

[spacester]

<b>GRAVITY LOSSES</b><br /><br />I'll be showing data for with or without gravity losses for three reasons.<br /><br />1) After making my claim to accuracy the other day (from which the previous post was adapted), I did a one-more-time review of my math, and I got to looking at the gravity losses – they look almost random at first glance and they are one of the most recent additions to the code. With orbital mechanics, odd patterns appearing to be random can happen, so it may or may not be a bad calc.<br /><br />The calculation of gravity losses is based on the sine of the angle of the thrust vector above the local horizontal. So if the angle is zero, the sine of the angle is zero and the gravity losses are zero.<br /><br />Now, everything moving in space is moving in an elliptical path. There is actually no such thing as a perfectly circular orbit. If you compare the tangent to a circle to the tangent to an ellipse at the same point and radius, you find they are slightly different. So in the real world, as you prepare to fire your rocket motors and you're wondering how much tax you're going to pay to Mr. Newton (gravity losses), it's worth understanding these angles.<br /><br />2) The calculation of gravity losses is based on instantaneous thrust, well not really but in practice pretty nearly. To be exact, you would need to know the effective thrust angle over the lifetime of the burn (ack! numerical integration!), but instead I'm just calculating with a static constant angle. This is simply the thrust angle from the local circular horizontal for an instantaneous burn. Which in reality will be timed with the burn halfway completed at the point in time where instantaneous thrust would be applied.<br /><br />So if you time your burn just right, you can make it so the average thrust angle is very nearly zero. (But it's not like the offline thrust before and after cancel each other – losses are losses.) This also requires that your departure vector is very nearly tangent to the pl <div class="Discussion_UserSignature"> </div>

 

[spacester]

OK maybe you thought those posts were long but that was nothing, here comes the raw data (2 posts). Then the summaries (2 posts). Then at last, the charts. <div class="Discussion_UserSignature"> </div>

 

[spacester]

Pre-summary datasets of gravity loss corrected Hohmann transfers to Mars follow.<br /><br />*************************<br />Away transfer insertion date is ........ 2005-AUG-13 03:07:45<br />Orbital insertion at destination date is 2006-MAY-22 07:03:24<br />Return transfer insertion date is ...... 2007-AUG-07 08:01:00<br />Orbital insertion at origin date is .... 2008-APR-05 02:26:54<br />Wait time prior to away mission is 359.9420 days,<br />Time of flight away mission is 282.1636 days, Hohmann flight<br />Stay time at destination is .... 442.0400 days, 64.3473 % of Martian year<br />Time of flight return mission is 241.7680 days, Hohmann flight<br />Total Mission time is .......... 965.9716 days<br />***Delta V values corrected for eccentric planetary orbits***<br />***Delta V values corrected for parking orbits around planets***<br />*Parking orbit at origin prior to away trip:<br /> Periapse altitude= 375 km, Apoapse altitude= 400 km<br />*Parking orbit at destination after away trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 50000 km<br />*Parking orbit at destination prior to return trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 600 km<br />*Parking orbit at origin after return trip:<br /> Periapse altitude= 475 km, Apoapse altitude= 500 km<br />**Target altitude at destination (impact parameter) = 6507 km<br />**Target altitude at origin (impact parameter) = 24000 km<br />***Delta V values corrected for gravity losses***<br /> Delta V for gravity losses, start of away mission = 0.1721 km/sec<br /> Delta V for gravity losses, end of away mission = 0.1259 km/sec<br /> Delta V for gravity losses, start of return mission = 0.2854 km/sec<br /> Delta V for gravity losses, end of return mission = 0.2601 km/sec<br /> Burn Time, start of away mission = 1800 sec<br /> Burn Time, end of away mission = 1800 sec<br /> Burn Time, start of return mission = 1800 sec<br /> Burn Time, end of retu <div class="Discussion_UserSignature"> </div>

 

[spacester]

Pre-summary datasets of non-gravity loss corrected Hohmann transfers to Mars follow.<br /><br />*************************<br />Away transfer insertion date is ........ 2005-AUG-13 03:07:34<br />Orbital insertion at destination date is 2006-MAY-22 07:03:13<br />Return transfer insertion date is ...... 2007-AUG-07 08:00:49<br />Orbital insertion at origin date is .... 2008-APR-05 02:26:46<br />Wait time prior to away mission is 357.2160 days,<br />Time of flight away mission is 282.1636 days, Hohmann flight<br />Stay time at destination is .... 442.0400 days, 64.3473 % of Martian year<br />Time of flight return mission is 241.7680 days, Hohmann flight<br />Total Mission time is .......... 965.9717 days<br />***Delta V values corrected for eccentric planetary orbits***<br />***Delta V values corrected for parking orbits around planets***<br />*Parking orbit at origin prior to away trip:<br /> Periapse altitude= 375 km, Apoapse altitude= 400 km<br />*Parking orbit at destination after away trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 50000 km<br />*Parking orbit at destination prior to return trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 600 km<br />*Parking orbit at origin after return trip:<br /> Periapse altitude= 475 km, Apoapse altitude= 500 km<br />**Target altitude at destination (impact parameter) = 6507 km<br />**Target altitude at origin (impact parameter) = 24000 km<br />Delta V for away mission, burn 1 = 3.7193 km/sec<br />Delta V for away mission, burn 2 = 0.5728 km/sec<br />Delta V for away mission, Total = 4.2921 km/sec<br />Delta V for return mission, burn 1 = 2.4628 km/sec<br />Delta V for return mission, burn 2 = 3.4387 km/sec<br />Delta V for return mission, Total = 5.9015 km/sec<br />Total Delta V for entire mission = 10.1936 km/sec Round Trip<br /><br />*************************<br />Away transfer insertion date is ........ 2007-SEP-17 06:44:38<br />Orbital insertion at destination date is 2008-JUN-23 16:48:01<br />Return tr <div class="Discussion_UserSignature"> </div>

 

[spacester]

Summary of gravity loss corrected Hohmann transfers to Mars follows.<br />The parking orbits and burn times remain constant and are shown in the first dataset only.<br />Certain other lines are deleted; refer to the pre-summary data sets as required.<br /><br />Away transfer insertion date is ........ 2005-AUG-13 03:07:45<br />Orbital insertion at destination date is 2006-MAY-22 07:03:24<br />Return transfer insertion date is ...... 2007-AUG-07 08:01:00<br />Orbital insertion at origin date is .... 2008-APR-05 02:26:54<br />Wait time prior to away mission is 359.9420 days,<br />Time of flight away mission is 282.1636 days, Hohmann flight<br />Stay time at destination is .... 442.0400 days, 64.3473 % of Martian year<br />Time of flight return mission is 241.7680 days, Hohmann flight<br />Total Mission time is .......... 965.9716 days<br />***Delta V values corrected for eccentric planetary orbits***<br />***Delta V values corrected for parking orbits around planets***<br />*Parking orbit at origin prior to away trip:<br /> Periapse altitude= 375 km, Apoapse altitude= 400 km<br />*Parking orbit at destination after away trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 50000 km<br />*Parking orbit at destination prior to return trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 600 km<br />*Parking orbit at origin after return trip:<br /> Periapse altitude= 475 km, Apoapse altitude= 500 km<br />**Target altitude at destination (impact parameter) = 6507 km<br />**Target altitude at origin (impact parameter) = 24000 km<br />***Delta V values corrected for gravity losses***<br /> Delta V for gravity losses, start of away mission = 0.1721 km/sec<br /> Delta V for gravity losses, end of away mission = 0.1259 km/sec<br /> Delta V for gravity losses, start of return mission = 0.2854 km/sec<br /> Delta V for gravity losses, end of return mission = 0.2601 km/sec<br />Delta V for away mission, burn 1 = 3.8915 km/sec<br />Delta V for away mission, burn 2 = 0.6987 km/ <div class="Discussion_UserSignature"> </div>

 

[spacester]

Summary of non-gravity loss corrected Hohmann transfers to Mars follows.<br />The parking orbits remain constant and are shown in the first dataset only.<br />Certain other lines are deleted; refer to the pre-summary data sets as required.<br /><br />*************************<br />Away transfer insertion date is ........ 2005-AUG-13 03:07:34<br />Orbital insertion at destination date is 2006-MAY-22 07:03:13<br />Return transfer insertion date is ...... 2007-AUG-07 08:00:49<br />Orbital insertion at origin date is .... 2008-APR-05 02:26:46<br />Wait time prior to away mission is 357.2160 days,<br />Time of flight away mission is 282.1636 days, Hohmann flight<br />Stay time at destination is .... 442.0400 days, 64.3473 % of Martian year<br />Time of flight return mission is 241.7680 days, Hohmann flight<br />Total Mission time is .......... 965.9717 days<br />***Delta V values corrected for eccentric planetary orbits***<br />***Delta V values corrected for parking orbits around planets***<br />*Parking orbit at origin prior to away trip:<br /> Periapse altitude= 375 km, Apoapse altitude= 400 km<br />*Parking orbit at destination after away trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 50000 km<br />*Parking orbit at destination prior to return trip:<br /> Periapse altitude= 500 km, Apoapse altitude= 600 km<br />*Parking orbit at origin after return trip:<br /> Periapse altitude= 475 km, Apoapse altitude= 500 km<br />**Target altitude at destination (impact parameter) = 6507 km<br />**Target altitude at origin (impact parameter) = 24000 km<br />Delta V for away mission, burn 1 = 3.7193 km/sec<br />Delta V for away mission, burn 2 = 0.5728 km/sec<br />Delta V for away mission, Total = 4.2921 km/sec<br />Delta V for return mission, burn 1 = 2.4628 km/sec<br />Delta V for return mission, burn 2 = 3.4387 km/sec<br />Delta V for return mission, Total = 5.9015 km/sec<br />Total Delta V for entire mission = 10.1936 km/sec Round Trip<br /><br />****************** <div class="Discussion_UserSignature"> </div>

 

[spacester]

OK now we can do two tables<br /><br />DeltaV for Hohmann transfer, km/second<br />From LEO (375 km x 400 km)<br />to HEMO (500 km x 50000 km Martian orbit)<br />Uncorrected for gravity losses:<br />Year. . . . . .Burn1. . . . . .Burn2<br />2005. . . . . .3.7193 . . . . . . 0.5728<br />2007. . . . . .3.7035 . . . . . . 0.6150<br />2009. . . . . .3.6341. . . . . . 0.9179 <br />2011. . . . . .3.5364. . . . . . 1.2450<br />2013. . . . . .3.4338. . . . . . 1.4017<br />2016. . . . . .3.3692. . . . . . 1.2708<br />2018. . . . . .3.5122. . . . . . 1.2991<br />2020. . . . . .3.6989. . . . . . 0.6929 <br />2022. . . . . .3.7181. . . . . . 0.5531<br />2024. . . . . .3.6659. . . . . . 0.7840<br /><br />DeltaV for Hohmann transfer, km/second<br />From LEO (375 km x 400 km)<br />to HEMO (500 km x 50000 km Martian orbit)<br />Corrected for gravity losses (burn time = 1800 seconds):<br />Year. . . . . .Burn1. . . . . .Burn2<br />2005. . . . . .3.8915 . . . . . . 0.6987<br />2007. . . . . .3.9580 . . . . . . 0.7793<br />2009. . . . . .3.8905. . . . . . 1.2923<br />2011. . . . . .3.7285. . . . . . 1.7178<br />2013. . . . . .3.4911. . . . . . 1.8275<br />2016. . . . . .3.5233. . . . . . 1.4142<br />2018. . . . . .3.7039. . . . . . 1.7556<br />2020. . . . . .3.8077. . . . . . 0.9578 <br />2022. . . . . .3.9516. . . . . . 0.6108<br />2024. . . . . .3.9298. . . . . . 1.0880<br /> <div class="Discussion_UserSignature"> </div>

 

[spacester]

OK I'm done for now. Questions? Discussion? <div class="Discussion_UserSignature"> </div>

 

[radarredux]

> <i><font color="yellow">OK I'm done for now. Questions? Discussion?</font>/i><br /><br />All I can say for now is "Wow! and Thanks!"<br /><br />It will take me a little while to absorb all this data.</i>

 

[halman]

spacester,<br /><br />I get the impression that either you have a LOT of time on your hands, or that you really enjoy math enough to run the progarm and THEN type the results in to the board.<br /><br />In either case, thank you for your devotion.<br /><br />Hohmann transfer orbits got a lot of press back when rockets were still having problems getting off the ground. Sending payloads to other planets would be possible in most cases only if the most economical methods were used. Everyone in the space travel field believed that by now, we would be using nuclear powered rockets which could move 10,000 ton payloads to Mars in two months. I think that they certainly would be distressed to find that we are having to play cosmic billiards to create spirograph trajectories to get payloads out of Low Earth Orbit!<br /><br />This is one of the reasons why the people advocating missions to Mars anytime before 2100 really bother me. Even if we still had the Saturn 5 around, we would be limited to a payload to Mars equivalant to the Apollo Command Module, Service Module, and Lunar Excursion Module, if we used Hohmann orbits. I think that there is a good probability that a Martian Excursion Vehicle will weigh at least 20 tons, and probably more. Landing on Mars will mean using atmospheric braking and rocket braking, because the ship will have to be able to take off again.<br /><br />Even if supplies are sent ahead of time, and include some kind of habitat, the Martian landing vehicle is going to be much larger than the LEM. And how large of a ship will be needed for the trip to Mars and back? This vehicle is going to be the living quarters for several people for months at least, and more probably, years! Some readers may remember the Gemini endurance missions, when NASA was trying to make sure that being in space for ten days or so would not do permenant harm to humans. Being in space won't, but ten days of nothing to do did. There were some morale problems, to say the least. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[spacester]

<font color="yellow">I get the impression that either you have a LOT of time on your hands, or that you really enjoy math enough to run the progarm and THEN type the results in to the board. <br /><br />In either case, thank you for your devotion. </font><br /><br />You're welcome; I appreciate the encouragement. I've been sick this week, so had a rare window of opportunity to tie up some loose ends. Soon my time for posting will become much more limited.<br /><br />I've got an ulterior motive – a master project - for all these posts I've been doing, plus I wanted to get some reference material posted for anyone interested. I'm just hoping there's some 10-year old math whiz with a Billionaire father lurking out there comprehending what I'm telling him . . . <img src="/images/icons/laugh.gif" /><br /><br />Seriously, I'm trying to show everybody that *you too!!* can sketch out mission designs and rocketship designs with relative ease and no calculus. Everything I've posted lately has been algebra and geometry.<br /><br />Another well written post with which I mostly agree. But as usual, I don't understand where you end up in the year 2100 before we can put together a proper Mars Mission.<br /><br /><font color="yellow">So it seems likely to me that a Mars mission will mean sending at least 100 tons from Low Earth Orbit, probably more. </font><br /><br />Oh, yeah, MUCH more than 100 tons IMO, I think we should send the first crew there in style, as much as a million kilograms (1000 tonne = 1102 ton) Yet another set of missions for the workhorse HLLV BDB we put together ASAP.<br /><br /><font color="yellow"> To SIGNIFICANTLY reduce transit times will mean significantly more delta-V, which means more mass leaving LEO. </font><br /><br />Give me some numbers and let's see just how much. You sketch out the mission and vehicle concepts and I'll help you develop your own little space program. Offer open to all, but act now for quicker response times! <div class="Discussion_UserSignature"> </div>

 

[spacester]

For example, <img src="/images/icons/laugh.gif" /><br /><br />Say we want to send 250 tons of water to HEMO. That's the payload, well that plus the tank to hold it and the other spacecraft systems attached to the tank. Add 15 tons for the tank itself. Another 35 tons for the engines, structure, other systems and some margin.<br /><br />WL = 250 ton<br />Wi = 50 ton<br />Wp = [(Wi * pf) + (WL * pf)] / (1 - pf )<br />The propellant tanks (not the water tanks) are empty, how much fuel do we need?<br />Max dV, arrival, Hohmann, corrected = 1.8 km/s<br />Aerobraking contribution: 1.0 km/s<br />Engine contribution: 0.8 km / sec = 800 m / s<br />Isp = 375 sec (Scientific Wild A$$ Guess)<br />pf = 1 - 1 / (e ^ (Vf / Ve))<br />Vf = 800 m / s <--- From the charts in the first post<br />Ve = 9.807 * 375 = 3678 m / s<br />pf = 0.195<br />Wp = [(250 * 0.195) + (50 * 0.195)] / (1 – 0.195 ) = 72.67<br />72.7 tons of propellant to arrive in orbit<br /><br />This was assuming this vehicle ("probe stage") was staged from the behemoth that pushes it to Mars ("boost stage"). Let's say LEO has a LOX/LH2 depot, so we get to employ Isp = 475 s engines. <br /><br />Run that same calc for the boost stage:<br />WL = 250 + 50 + 72.7 = 373 ton<br />Wi = 75 ton (Scientific Wild A$$ Guess)<br />pf = 1 - 1 / (e ^ (Vf / Ve))<br />Vf = 4.00 km / s <--- From the charts in the first post<br />Ve = 9.807 * 475 = 4658 m / s<br />pf = 0.576<br />Wp = [(373 * 0.576) + (75 * 0.576)] / (1 – 0.576 ) = 608.9 ton<br />609 tons of propellant to send the probe stage to Mars, which burns only 73 tons of (storable) prop at arrival. <br /><br />The behemoth booster could do a gravity assist to get back home to cislunar space and various tricks employed to get it back to LEO with minimum dV for a second mission. The Payload mass would be zero, Wi = 75 ton would include prop margin. dV is unknown for the moment.<br /><br />The water tank would stay in Martian orbit and have enough dV margin to ease the rendezvous dV burden for the thirsty vessels it <div class="Discussion_UserSignature"> </div>

 

[igorsboss]

Wow.<br /><br />Page 12, line 18, the '1.344' should have been '1.348'.<img src="/images/icons/wink.gif" />

 

[halman]

spacester,<br /><br />Thank YOU for the affirmation! I love to write, (as you may have noticed,) and I know that I am guilty of running my mouth off at times. I am trying to keep my posts concise and to the point, and to break up the text into smaller blocks so that it is not so hard to read. I have really enjoyed many of the 'conversations' that have happened on this board, because there are very few people I meet in my daily life who are interested and informed about space flight. (Hint! Hint, to those of you lurking out there!)<br /><br />Because I believe that outer space offers solutions to many of the problems that we currently face here on Earth, I am most interested in seeing rapid development of off-planet mining and manufacturing. To me, this takes precedence over exploring other the planets at this time, because we are not in any position to be able to utilize resources at the bottoms of deep gravity wells. For the immediate future, the Moon and the Asteroid Belt contain all that we need to establish a dynamic economy in space.<br /><br />You question where I came up with the date 2100 for the earliest feasible manned mission to Mars. That is a totally of the top of my head guess, which I can not defend beyond to say that if we are going to go to the trouble of sending people that far away, we should wait until we have the ability to do it royally. Certainly, our technology is capable of mounting a mission long befere then. But it is very unlikely that it would be the beginning of a sustained effort to develop Mars for human habitation, or that it would produce a large amount of science.<br /><br />There is a huge gap between our technical ability and our finacial wherewithal right now. We undoubtably have the ability to build a permanent base on the Earth's moon within 25 years, but it would require a tremendous increase in the amount of money that our government is spending on space. But I strongly believe that such a base will be built, perhaps in p <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[arobie]

Spacester, Wow and Thank You, but being a high school kid, I don't understand most of it. But I really do want to understand it. I'm apologize for my upcoming "dumb" questions.<br /><br />First of all, could you explain what a Hohmann transfer is to me? I had never heard of it before now, and I don't want to draw the wrong conclusions from reading data that I don't understand as of now.

 

[spacester]

Hey Arobie, well my short answer is that the Hohmann transfer is the longest trip time for a particular trip.<br /><br />Everything in the solar system orbits the sun, right? Since their are no truly perfectly circular orbits, everything is traveling in an eliptical path. You can draw an imaginary path in space that the planet travels along, this curve is an ellipse, and we call it the planet's orbit.<br /><br />Well if you want to go from one planet to another, you're still going to be orbiting the Sun, right? You'll still be on an ellipse. The Hohmann transfer is one possible elliptical path to go from one planet to another.<br /><br />The Hohmann transfer is the choice that takes the most time to make the journey. You should never have to take longer than the time it takes to do a Hohmann transfer. If you spend just a little more energy than for Hohmann, you get there faster.<br /><br />Beyond that, go ahead and google "Hohmann Transfer" and see the first three or more results. <div class="Discussion_UserSignature"> </div>

 

[arobie]

Thank You, that clears up ALOT. <br /><br />As I'm reading through the data, the next question I have is what does the acronym HEMO stand for?

 

[spacester]

Ah, excellent question! This is a clear indication that you are in fact reading the material. Excellent.<br /><br />HEMO - Highly Eccentric Martian Orbit<br />I've based these transfers on inserting into an orbit around Mars that requires less deltaV than a LMO<br /><br />LMO - Low Martian Orbit<br /><br />At the end of the Hohmann transfer, you get close enough to Mars to feel its gravity. If you are targeted just right, your path becomes bent just right so that you will fly by fairly close to the planet. If you don't burn your engines, this is just like a gravity assist maneuver.<br /><br />But we're going to burn our engines so that the moment in the middle of the burn is the point where we make the closest approach to the planet. This will slow us down enough to be captured by Mars and that means we are in orbit around Mars.<br /><br />We didn't kill more of our energy than we had to so we're going to go flying out a long ways from Mars again before coming back down to the same altitude as where we burned the engines. This means our Martian orbit is highly eccentric, IOW a HEMO.<br /> <div class="Discussion_UserSignature"> </div>

 

[najab]

Of course, aerocapture would significantly reduce the propellant requirements.

 

[cybersix]

"Say we want to send 250 tons of water to HEMO"<br /><br />250 tons in one shot?? So I guess the consensus around here has pretty much burned and buried the CFM <img src="/images/icons/frown.gif" />

 

[arobie]

Thank you very much more the answer. That clears up alot. All this data is just beginning to make sense.<br /><br /><font color="yellow">DeltaV for Hohmann transfer, km/second <br />From LEO (375 km x 400 km) <br />to HEMO (500 km x 50000 km Martian orbit)</font><br /><br />My next question is what are the "375 km x 400 km" and the "500 km x 50000 km"? What are they representing?

 

[najab]

When someone says a 100x200 orbit they mean that the low point of the orbit is 100 and the high point is 200. For a perfectly circular orbit the two numbers would be the same: 100x100, a highly eliptical orbit would have a big difference between the two numbers: 100x10000 for example.

 

[arobie]

Ok, Thx Najab.