ExoMars successfully completes long mid-course burn

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ExoMars 2016, the European/Russia orbiter/lander mission on its way to Mars, successfully completed a 52 minute mid-course engine burn today in preparation for its October 19th arrival at Mars.

Officially known as the deep-space maneuver, DSM, it was the longest engine burn for the ExoMars-2016 mission before the Mars orbit insertion on October 19, 2016. As a result of the July 28 orbit correction, the spacecraft will need less propellant during its maneuvers in the vicinity of the planet and the Schiaparelli lander will experience slightly less thermal loads during its planned entry into the Martian atmosphere.


  • Calvin Dodge

    A 52-minute midcourse correction burn? Doesn’t NASA usually do better than that?

  • Calvin Dodge: Do not assume that the length of this burn was because the spacecraft needed to make a gigantic correction. The length was determined by many factors, all of which appear planned, including the overall thrust of the engine itself.

  • Edward

    Interestingly, Mars missions usually no longer use the Hohmann Transfer Orbit, which takes about 9 months, but use a faster transfer orbit, taking closer to seven months.

    This link should give better details:
    “28 July (forecast): TGO carries out one of the most critical activities during the voyage to Mars: a very large engine burn in deep space that changes its direction and speed by some 326 m/s. This midcourse trajectory correction will line the spacecraft up to intersect the Red Planet on 19 October.”

    As we improve space navigation and operations, with increasingly reliable spacecraft, we advance from flybys to complex maneuvers — including aerobraking — to reach the orbits we want.

  • Localfluff

    It cannot be a pure Hohmann transfer given this burn, by I think it is pretty close. Only electric propulsion would not use Hohmann transfers to Mars. The travel time varies with the distance to Mars at conjunction, which varies substantially due to Mars’ eccentricity. For example, Mars is 75% further away, when at closest during conjunction years, in 2027 than in 2018. Some years have 6 months travel time, others have 9 months and it varies cyclically with a period of about 7 conjunctions as Earth running passed Mars. The total travel time Earth-to-Earth is the same. The difference is in how long one spends at Mars instead of transferring in interplanetary space. 2033 and 2035 look good for human spaceflight to Mars.

  • Localfluff

    Here’s a text about “oppositions of Mars” and a table:
    (There is confusion in what is opposition and conjunction. I call it conjunction when Earth and Mars line up on the same side of the Sun. Others call it opposition because Mars is then on the opposite side of Earth from the Sun.)

  • Edward

    “Pretty close” is a miss. It’s main relationship to a Hohmann transfer orbit is that both are elliptical.

    The Hohmann transfer orbit (HTO) was first proposed as a minimum energy orbit (propellant expenditure) to change from planet to planet, such as from Earth to Mars. The origination and destination orbits need not be circular. This transfer orbit can also be used to go from low Earth orbit (LEO) to geostationary orbit or to change other orbital heights. HTO is defined as an orbit in which the ellipse of the orbit is at periapsis (perigee, perihelion, etc.) at the lower orbit and at apoapsis at the higher orbit, whether transferring up or down. Thus, inserting into HTO from the origination orbit is done 180 degrees away from inserting into the destination orbit, and insertion and arrival are tangent to both the origination and destination orbits.

    At ExoMars arrival, Mars is around 135 (not 180) degrees from the Earth at launch, as shown below, taking less time to reach Mars than the HTO takes. Thus, the transfer orbit used is not a Hohmann Transfer Orbit, although it is elliptical (except for the adjustment made a few days ago, but the current orbit is also elliptical). Constant electric propulsion would not be an elliptical orbit.
    https://www.youtube.com/watch?v=ZEb6kEKFuTk (1/2 minute)

    As we can see, ExoMars did not leave Earth in an orbit tangential to Earth’s orbit.

    I have not studied the orbital transfer that ExoMars is using to get to Mars, but my understanding is that the reduced travel time does not require much more additional propellant, overall, than the HTO would use.

    There are three major phases in transferring between planets. Phase 1 is when the first planet’s gravity is dominant, phase 2 the Sun’s gravity is dominant, and phase 3 the destination planet’s gravity is dominant. The video above shows the entire transfer from the Sun’s point of view, but we could have looked at it from all three points of view.

    Around the Earth, the probe starts at LEO at 5 miles per second. It is accelerated by 2 mps to reach escape velocity, plus another couple of miles per second to climb the Sun’s gravity well to Mars’ orbit.

    Around the Sun, it takes an elliptical orbit toward Mars, slowing as it climbs (trading velocity for height from the Sun), then for ExoMars, there was the adjustment burn on July 27th, and finally arrival into Mars’ gravitational influence in late September or early October.

    Around Mars, another burn is necessary to enter Martian orbit, but as seen from Mars, the probe is travelling at escape velocity, and the probe has to slow down relative to Mars (the Sun would see it as speeding up) in order to get into orbit around Mars.

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