DeCaf The man who runs round the world to spread peace

the biological impact of exposure to radiation in space, there is also subjectivity in defining how much risk is appropriate. Presently, there are no guidelines for allowable radiation exposure in deep space. Most of the existing data and understanding of radiation effects relates to X-ray and gamma-ray exposure, and relatively little is known about continuous low dose rate heavy-ion radiation.

It is a known fact that the human body undergoes certain changes when exposed to extended periods of weightlessness — changes that are most debilitating when the space traveller must readapt to gravity. The most serious known changes include cardiovascular deconditioning, decreased muscle tone, loss of calcium from bone mass, and suppression of the immune system. A variety of countermeasures for these conditions have been suggested, but none have been validated through testing over a long term.

The experience with astronauts and cosmonauts who spent many months suggests that if the crew is not provided with artificial gravity on the way to Mars, they will arrive on another planet physically weak. Artificial gravity is often put forward as a possible solution. In this case, the entire spacecraft, or at least that portion containing the living quarters for the crew, would be rotated so that the crew experiences a constant downward acceleration that simulates gravity. It is generally assumed that the Coriolis effect (the dizziness caused by spinning around in circles) will fall below the threshold of human perception if the spacecraft is rotated at a slow rate. It is not known whether simulation of full terrestrial gravity is required to counteract all of the known deconditioning effects of weightlessness, or whether the small residual Coriolis effect will cause some disorientation in crew members. No data from a space-based facility exists. DECCAN CHRONICLE manoeuvre and to manoeuvre the surface systems into the appropriate relative position at the surface outpost. The descent stage may consist of four subsystems: a basic structure to which all other elements (including payload) are attached, a parachute system to assist in slowing the stage, a propulsion system to slow the stage prior to landing, and a surface mobility system. The use of parachutes has been assumed to help reduce the descent vehicle’s speed after the aeroshell has ceased to be effective and prior to the final propulsive manoeuvre. Sufficient atmosphere is present for parachutes to be more effective than an equivalent mass of propellant. The propulsion system employs engines to perform the post-aero capture/or deboostburn and to perform the final manoeuvre, prior to landing on the surface. Once on the surface, the lander moves limited distances to compensate for landing dispersion errors and move surface elements into closer proximity.

When the surface mission has been completed, the crew must rendezvous with the orbiting Earth Return Vehicle. This phase of the mission is by the Mars Ascent Vehicle (MAV) which consists of an ascent propulsion system and the crew ascent capsule. The MAV is delivered to the Mars surface atop a cargo descent stage. The ascent propulsion system is delivered with its propellant tanks empty.

However, the same descent stage also delivers a nuclear powersource, a propellant manufacturing plant, and several tanks of hydrogen to be used as feedstock for making the required ascent propellant. This approach was chosen because the mass of the power source, manufacturing plant, and seed hydrogen is less than the mass of the propellant required by the ascent stage to reach orbit. Not carrying this propellant from Earth will give the mission the flexibility to send more surface equipment to Mars or to use smaller launch vehicles or some combination of the two options.

The crew rides into orbit in the crew ascent capsule. Life support systems are designed for the relatively short flight to the waiting ERV. The ascent vehicle will need to use locally sourced oxygen and methane to lift the payload from the Mars surface to orbit. Then the vehicle will dock with the inspace propulsion and deep space habitat in the Mars orbit to travel back to Earth orbit where it will safely land the crew back on Earth’s surface. In case of a mission abort due to any contingency it becomes necessary to remain in the Mars vicinity for a considerable length of time (typically 500±600 days, depending on specific launch date) before attempting to return.

The Life support for an additional 500±600 days must be added to the Earth Return Vehicle to support the crew in orbit for that period, thus driving up the mission mass and cost. The requirements for fail-safe life support for a crew will be very significant and challenging. The crew will be exposed to excessive radiation for the additional 500±600 days in orbit, having lost the benefits of (a) shielding by the planet from below,(b) shielding provided by the atmosphere, and (c) possible use of regolith piled on top of the Habitat as shielding. (Mylswamy Annadurai is Director, UR Rao Satellite Centre — formerly Isro Satellite Centre, Bengaluru) WEDNESDAY | 29 AUGUST 2018 | HYDERABAD