The Eve Express Mission
Continuing the robotic exploration of the solar system
After the success of the Duna Express Mission, the next target of the agency's robotic exploration program was Kerbin's other planetary neighhbor: Eve. Slightly larger than Kerbin itself, Eve is peculiar for its extraordinary atmosphere. Being five times denser at the surface and about 50% thicker, Eve's atmosphere makes it a prime target for aerobraking maneuvers.
The Eve Express Mission would expand on the achievements of its Duna predecessor by landing a robotic rover to the surface, instead of just an immobile lander. Eve's thick atmosphere makes parachute descent possible, which is simpler than powered descent. The rover was to take a full suit of scientific instruments to study the physical and chemical composition of Eve's atmosphere and surface.
In addition to landing a rover and putting a reconaissance satellite in low Eve orbit, the mission would also aim for Eve's small satellite, the captured asteroid Gilly. Due to its eccentric orbit around Eve and its tiny sphere of influence, Gilly represent a challenge in orbital mechanics. The huge delta-v requirement of about 1900 m/s to reach the small moon from Eve orbit necessitated attaching a booster stage to the reconaissance satellite.
The following were the stated objectives and details of the mission:
- Eve Express Mission
- Primary Objectives:
- Putting a reconaissance satellite in a low Eve orbit.
- Putting a reconaissance satellite in a low orbit around Gilly.
- Delivering a robotic rover to the surface of Eve.
- Details:
- Total Payload Mass: 2260 kg (satellites and rover)
- Satellites Mass: 270 kg sat + 410 kg booster (each)
- Satellites Δv: 753 m/s sat + 1485 m/s booster
- Rover Mass: 770 kg rover + 130 kg heatshield
- Rover Power Reserve: 335 E
- Rover Power Plant: 8 x solar panels (158 E/min max at Eve, each)
- Rover Backup Power: 1 x RTG (45 E/min)
- Transfer Stage Mass: 3530 kg
- Transfer Stage Δv: 1636 m/s
- Total Spacecraft Mass: 5.79 tons
- Transfer window center: Year 1 Day 147 12h 09m
Having developed the confidence to do so, for the first time mission planners had the interplanetary transfer rely heavily on aerobraking for orbital insertion. With the payload attached, the Eve Express transfer stage has a total delta-v of 1636 m/s. However, the Eve transfer requires about 1050 m/s and the Eve insertion another 1310 m/s. Thus, the Eve Express spacecraft does not have enough fuel to complete a powered orbital insertion after intercepting Eve.
The mission thus mandated the execution of several aerocapture/aerobraking maneuvers. The plan was to first perform an aerocapture into a high elliptic orbit around Eve, and then use successive aerobraking passes to lower the apoapsis into low Eve orbit. Because aerobraking calculations are still experimental, this multistep plan was safer than betting everything on a single aerobraking pass, for the parameters could be adjusted as the mission developed and calculations were updated.
The Eve Express robotic probe is a multi-component spacecraft:
The first component is the Eve surface robotic rover:
Designed to operate autonomously on the surface of Eve, with additional commands sent through its comm link by operators on Kerbin, the rover is capable of functionning for extended periods of time during the day thanks to its ample base of solar panels and continue low-power operations during the night using its backup radioisotope thermoelectric generator. Its suite of scientific instruments allow performing atmospheric as well as geologic measurements.
The rover is mounted on top of a dettachable heatshield in order to whitstand the heat of reentry through Eve's thick atmosphere:
Since Eve's atmosphere is so dense, the final descent of the rover will be achieved with a single parachute. Predicted terminal speed near the surface is around 3.5 m/s at sea level. The rover wheels and suspension are designed to tolerate an impact up to 10 m/s.
The next two components are the twin reconaissance satellites destined for low Eve and Gilly orbits:
Sporting advanced topographic mapping instruments, they have a small fuel supply intended for small orbital adjustements and general stationkeeping. Due to Gilly's eccentric orbit and small sphere of influence, The Gilly satellite required an additional booster stage in order to reach its target. The booster stage triples the satellite's delta-v and was tailored to just reach Gilly from low Eve orbit. Because the additional weight would unbalance the spacecraft, the Eve satellite was also fitted with an identical booster stage even if its mission profile didn't require it. The unneeded booster would remain attached to the main spacecraft and function as a fuel reserve.
The final component is the small interplanetary transfer stage (weighing just slightly more than its payload), designed to deliver the payload to Eve orbit by taking full advantage of Eve's dense atmosphere through aerobraking maneuvers.
Due to the spacecraft's low total mass (as compared, for instance, to the Duna Express spacecraft's 8.4 tons), the launch rocket was fairly small:
Continue to Eve Transfer ...