Europe’s Trace Gas Orbiter has passed its check out


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Europe’s ExoMars 2016 Trace Gas Orbiter has completed its science instrument checkout in Mars orbit and will now begin a year of aerobraking to lower its orbit.

When the aerobraking is completed they will settle into a 250-mile circular orbit to study the Martian atmosphere.

14 comments

  • LocalFluff

    I thought the main point with aerobraking was to enter orbit from a high speed transfer trajectory. But they only start aerobraking now, in order to lower the orbit? Anyway, it’s good to see aerobraking being used. The fact that all planets (except Mercury) have atmospheres is very helpful for saving fuel reaching them with orbiters and landers. And a copy of the Trace Gas Orbiter would be nice to have at Venus too, but there seems to be some kind of global conspiracy against exploring Venus, I suspect the Martians are behind it.

  • Dick Eagleson

    Probably orbital mechanics behind it. It takes more delta-V to get to Venus than it does to get to Mars with a given mass.

  • LocalFluff

    “It takes more delta-V to get to Venus than it does to get to Mars with a given mass.”
    No, it doesn’t.
    How would you argue for that?
    You might have been confused by some raw astronomical data about delta-v required to launch from Venus surface (which truly would be very hard), but entering its orbit is much easier.

  • Edward

    LocalFluff wrote: “I thought the main point with aerobraking was to enter orbit from a high speed transfer trajectory.

    That is an excellent use for aerobraking, but it can also be used to lower the apoapsis (apogee) of an orbit,* especially a highly elliptical orbit.

    As for the Mars-Venus delta V debate, I decided to look for someone else’s work rather than dredge up the equations and work it out (lazy me). It looks like it is a wash, and it does not much matter.
    http://space.stackexchange.com/questions/2156/does-a-mission-to-venus-orbit-require-less-propellant-than-a-similar-mission-to
    Bottom line is, it takes more Delta v to orbit Venus because of it’s higher gravity. But what if you are willing to accept a higher orbit? The minimum orbit is a capture orbit. Venus has a delta V of 0.4 km/s, while Mars requires 0.7 km/s. Thus, the minimum orbit is slightly easier for Venus than Mars, but if you want to get in to a better orbit, Mars is easier. If you use aerobraking, then Venus becomes slightly easier.

    Wikipedia gives nice tables for various destinations:
    https://en.wikipedia.org/wiki/Delta-v_budget#Interplanetary

    If you are looking for an answer for Venus flyby to get to Mars, that may be a different matter, but keep in mind that a Venus flyby will increase the travel time.

    * This chart shows that it is called the apoareion for Mars:
    https://en.wikipedia.org/wiki/Apsis#Terminology_graph

  • wodun

    The answer is a little counter intuitive but I don’t understand orbital mechanics well enough to explain it correctly.

  • wodun

    Annnnd I should have refreshed before posting.

  • LocalFluff

    Edwards,
    The difference in delta-v between Mars and Venus is not as clear as I thought, different tables have different numbers. I suppose that it depends on how and when it is done. Venus’ higher gravity should be an advantage for an orbiter. Both should have equal benefits of aerobraking, since that is done in the very thin upper atmosphere (maybe a larger planet has geometrical benefit?). Venus at least has the advantage of shorter travel time and more frequent conjunctions, but not necessarily an advantage in delta-v. I think one has to look at real missions launched rather than tangle up in the details of assumptions for some general theoretical delta-v figure.

  • Dick Eagleson

    Mea culpa, Localfluff. I went looking for where I thought I had read that thing about Venus and it turned out to actually be about Mercury. As Emily Litella used to say on SNL, “Oh. That’s very different. Never mind.” I’ll plead an attack of senior-moment-itis. Edward is right. Venus and Mars are pretty much in a dead heat anent delta-V.

  • LocalFluff

    Mercury is hard to reach. Only two spacecrafts have ever gone there, the first was just a “clipper” (I suppose that has become a new term along with flyby, orbiter, lander and rover) that passed it by a couple of times. von Braun brought a pal named Ericke who suggested going to Mercury (or to the Sun) via a Jupiter gravity assist that would halt its Keplerian speed and let it dive into the gravity well. So, going 5 AU out in order to get 1 AU inwards.

    Solar Probe Plus (I think my detergent also is brand named “plus”) will launch Summer next year, to the Sun’s Corona. On a delta IV Heavy, the most powerful and expensive launcher in existence today. Not by Jupiter, but by no less than seven Venus flybys to gradually put Icarus’ wings in the fire.

    ESA’s Bepi Colombo probe to be launched in a year and a half will make a whole lot of gravity assists at Earth and Venus and at Mercury itself before it enters Mercury’s orbit 7 years later.

    This is why the Moon argument wins. You can go to it whenever you want, daily launch windows. And no gravity assists around some other planets. And you can be home again within a week. You can survive on a candy bar and we can save a shitload of monies by having the astronauts wear diapers (and use a bottle, with a funnel for the women) instead of installing a microgravity toilet in the spacecraft. Space is a great entertainment experience for tourists! Once in a lifetime (because you won’t pay for doing it again, oh well, some will).

  • Edward

    LocalFluff wrote: “This is why the Moon argument wins.

    There are many winning reasons for going to the Moon, even for going to the Moon before going to Mars. However, Mars has several advantages for long term, independent survival that do not exist on the Moon.

    I am very glad, though, that the NewSpace leaders are choosing to work on both destinations simultaneously, as this eliminates the need for the debate and ultimate (and likely delayed) decision between the two. The new space race answers the question of which body will have a colony first, and it is an unseen, unacknowledged, unrewarded race between private organizations rather than between governments.

  • LocalFluff

    Edward,
    Of course both the Moon and Mars will be explored and very possibly settled. And I think that free floating space stations will be the big thing in the far future. Completely engineered environments, paradises created in the nothingness. Planetary, lunar and asteroidal surfaces are dangerous because of gravity and chemistry and won’t be visited by people much more than people enter mines and caves on Earth today. To do specific work (or as a tourist experience). And asteroid mining will be big, that’s the place to go for materials, not to deep gravity wells. But that is not where it can start, the Moon comes first.

    The Moon versus Mars debate is a bit silly, lets just start with the Moon, it’s here in our corner of space. I love Mars but the Moon comes first, it is pretty obvious from pure geometry or looking at a map. Mars will take longer and I’m impatient, I only have one lifetime (as far as I know). Regardless of first destination, a decision has to be made now finally 56 years after the last decision on the subject. We’ll see if the new White House is capable of it. Just pick one and go for it and I will applaud it as long as it is doable within 10 years. Or maybe private entrepreneurs will do it, but in spite of all the good things going on on that front, that is still a too good vision for me to really believe in until I see it.

  • Dick Eagleson

    Localfluff,

    Good stuff about Von Braun and Krafft Ehricke. That’s just the sort of counter-intuitive thing that makes so much about traveling in space a pursuit that often lies well outside of Earth-centric “common sense.”

    I completely endorse your notion about where the main future of space settlement lies and your prudent admonition about avoiding steep gravity wells whenever reasonably possible.

  • Edward

    LocalFluff wrote: “So, going 5 AU out in order to get 1 AU inwards.”

    I think LocalFluff already knows this, but for everyone’s benefit:
    The closer you get to the sun, or any gravitational body, the deeper the gravity well and the steeper the sides, or the gravitational pull. This means that you need additional delta V to slow down at your destination, such as Mercury.

    To show how dramatic this well is, solar escape velocity from an orbit at Earth’s distance from the sun is about 43 km per second. However, escape velocity from the surface of the sun is somewhere around 600 km per second (my memory is hazy on this, but I seem to remember 625 km per second). This is the speed that a solar flair would need to be going in order to escape the sun’s gravity.

    Thus, as a spacecraft nears the sun, it gets going very fast, requiring a large delta V to slow down at Mercury (about .4 AU from sun), which travels about 47 km per second around the sun. Compare this to the Earth (1 AU), which travels about 30 km per second, or Jupiter (5 AU), which travels about 13 km per second.

  • Edward

    LocalFluff,
    The Moon/Mars debate may be silly, but it has been bypassed. Robert Zubrin showed a cost effective way to start with Mars sooner than any large, expensive governmental project would be able to do, and there are private organizations taking the lead on doing Mars sooner rather than later. They know Mars will take a long time, but like you, they are impatient to get there.

    Starting sooner will allow for a colony to start sooner, so these people want to get started now.

    Have no fear, the Moon’s advantages have other people’s attention. This time, the race to the Moon is between governments and private organizations.

    Arguing or suggesting that the Moon should be first misses the point that there are people who are determined to get to Mars during our lifetimes. The argument is now moot, and suggesting the Moon be first is pointless. In a few years it may even be pointless to suggest that governments should spend resources going to the Moon, as private organizations just might get there before the governments do.

    One of the early profitable activities for these private organizations on the Moon is to supply relatively inexpensive propellant for those going to Mars.

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