Entry and Landing Systems

Arrival at Venus

Once the spacecraft enters into orbit around Venus, the craft will stay in orbit until its next closest approach with the Earth. The planet will begin to catch up to the Earth, and at that time the Venus orbiter will launch the landing probe toward the surface. It was decided that the craft would launch at this time so that the landing probe will be exposed to the surface environment only when the Venus-Earth communications link is up and running for the transfer of geological data via the seismic sensor. The plan calls for the probe to be exposed to the extreme surface conditions only for the minimum amount of time needed for the mission (only 90 days).

The probe will be housed inside of an ablative entry shield that will allow for successful planetary reentry. Ablation is basically the removal or melting away of an expendable part, this case being the front cone of the heat shield. The entry probe will enter the Venusian atmosphere at an extremely high velocity. This will cause the atmospheric gases to heat up and ionize through friction, raising the temperature and pressure in front of the ablative shield and cause material to melt and be carried away by the oncoming flow of gas. The ablative properties will allow the craft to reliably land on the surface without damage to its internal operations and electronics. The cone angle needs to be equal to 45 degrees so that the probe will be stable in the hypersonic and supersonic regions [1, 2].

Figure 1: Entry Probe Concept [2]

The ablation material used for this mission will be PICA, which is a very low density, high performance material capable of withstanding temperatures of 1,930 degrees Celsius [1]. It was also used on the Mars Science Laboratory mission and the Stardust mission performed by NASA. PICA stands for “Phenolic Impregnated Carbon Ablator” [1]. Basically a phenolic polymer is injected with carbon in order to strengthen the already resilient material, resulting in a material that can be placed into tiles to be placed on the surface of the Venus probe heat shield. Based off of the ratio of the Mars Curiosity Rover’s area to the Rover’s Heat Shield, it was estimated that the heat shield diameter for the Venus probe should be about 3.436 meters.

Once the probe slows down considerably, a parachute will deploy that will cause a further reduction in velocity for the Venus landing probe. The remainder of the heat shield will then be ejected so that the craft will be able to land upright on its own base structure located on the bottom of the probe [2]. The landing legs of the craft will be wide enough so that the lander will have a very high probability of landing upright on the surface of Venus [3]. The figure below shows a similar lander design mocked up by NASA in 2010. 

Figure 2: Landing Configuration [3]

References

(1)    Stackpoole, M., et. Al. “Low Density Carbon Phenolic Ablators.” NASA Ames Research Center. http://www.planetaryprobe.org/sessionfiles/Session7A/Posters/Stackpoole-Poster.pdf.

(2)     Van der Berg, Et. Al. “ESA Venus Entry Probe Study.” 2nd international Planetary Probe Workshop NASA Ames Conference Centre. http://sci.esa.int/future-missions-preparation-office/37072-esa-venus-entry-probe-study/. April 25th, 2005.

(3)    Dyson, Roger W. and Geoffrey A. Bruder. “Progress Towards the Development of a Long-Lived Venus Lander Duplex System.” NASA Glenn Research Center. 2011.