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ESA Document - Emits - ESA

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2.4.3.5 TEI and planetary protection<br />

HMM<br />

Assessment Study<br />

Report: CDF-20(A)<br />

February 2004<br />

page 35 of 422<br />

If TEI is broken into phases to allow for a staged approach, then it must be ensured that the<br />

jettisoned first stage does not impact the surface of Mars within 50 years. The escape manoeuvre<br />

must be biased such that the escape stage does not hit the Earth. The THM must then be<br />

redirected to a trajectory closer to the Earth. This adds to the THM budget.<br />

2.4.3.6 Final retargeting and Earth arrival<br />

Designing this phase implies striking a balance between maximizing protection of the Earth and<br />

maximizing crew safety. The strategy assumed for the return trajectory is shown in Figure 2-14.<br />

The TEI dispersions are corrected with the retargeting manoeuvre seven days after Mars escape.<br />

The trajectory still is fail-safe and Earth-avoiding. Any failure at this time will lead the THM<br />

past the Earth.<br />

Sixty days prior to the nominal arrival, at a distance of 18 million km, if the spacecraft is still<br />

functional, a retargeting is performed. Optionally, at this time the longitude and latitude of the<br />

touchdown point can be changed. One day prior to arrival, the crew moves to an Earth entry<br />

capsule and separates from the THM.<br />

Figure 2-14: Earth Return Trajectory Strategy<br />

There are two options for the final phase:<br />

• At the retargeting 60 days before arrival, the THM can be targeted for an entry orbit.<br />

Then, after the entry capsule is separated one day before entry, the THM must be moved<br />

to a trajectory with a slightly higher perigee so that is passes by the Earth<br />

• Alternatively, the retargeting can send the THM on a trajectory that passes close to the<br />

Earth without entering the atmosphere. Then, after the entry capsule is separated, it must<br />

navigate itself to an entry trajectory<br />

2.4.4 Budgets<br />

2.4.4.1 Earth escape window<br />

• Escape window: 08/04/2033 – 28/04/2033<br />

• Hyperbolic escape velocity: 3.022 – 3.200 km/s

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