Tuesday, June 10, 2014

The ESA, the Venusian Summer & aerobraking

The Venus Express for all the learning about Venus and her ionosphere and atmosphere is preparing to take the plunge sometime this summer. No, not into a refreshing pool, but into the atmosphere where it is expected she will burn up.


It’s been eight years of study, a doctorate or at the very least a masters degree in the Venusian atmosphere plus. Alas propellant only lasts so long and so the ESA is seeing it as an opportunity instead of a sad goodbye. The Venus Express is going to take one last maneuver so that the ESA can gain the knowledge on a technique which they hope to use on later missions – aerobraking; a way of slowing down spacecraft approaches without necessitating expensive retro rockets and propellants.

ESA sees aerobraking as a way of slowing down arriving spacecraft without heavy and expensive retro rockets and propellants. When an interplanetary vehicle reaches its destination its velocity must change in order to remain in the vicinity of the particular body/planet/moon etc. In order to accomplish a low, near circular orbit as might be desired for any of the probes sent for scientific study, there is a velocity shift of several kilometers a second. Propulsion cannot be used as then a large fraction of the spacecrafts mass will be the fuel required. 

Needed is a target body that has an atmosphere.

First one uses a relatively small burn to allow the spacecraft to be captured in the elliptical orbit. Then the aerobraking is used in order to circularize the orbit. There are two options for how much is enough. If it is a thick atmosphere ten a single revolution might do the trick; but if it is done in the higher and subsequently thinner region of atmosphere then many passes are required. Aerobraking is, besides the fuel benefits,  an attempt to reduce the frictional heating. Due to the unpredictable nature of turbulence effects, varying atmospheric composition, and temperature, the one revolution is rarely the case. In fact often aerobraking takes six months worth of passes. (several hundred if we’re talking about the moon)

So somewhere between July 18th and 11th the ESA will be continuing to take readings via Venus Express, but also beginning the aerobraking experiment. Its not likely to survive the aerobraking but on the outside chance that it does; well, its final fate is a plunge into the atmosphere where it will burn up.

According to ESA, the aerobraking experiment will take place sometimebetween June 18 and July 11, during which the spacecraft’s instruments will continue to take readings of the atmosphere and surrounding conditions. The agency is not certain if the Venus Express will survive the experience, but if it does, its condition will be assessed before the decision is made whether or not to extend the mission for a few more months. Either way, Venus Express’ ultimate fate will be a final plunge into the atmosphere, where it will burn up.

No comments:

Post a Comment