February 1983:space activities report

MORE SHUTTLE ASTRONAUTS

NASA has decided to relax some of their requirements for flying people aboard the Space Shuttle. Until now, flight opportunities for Payload Specialists have been offered to customers buying a half or more of a Shuttle mission or who were flying a unique experiment needing the unique talents of a particular scientist or engineer.

Under the expanded programme, to begin in 1984, that will change. Flight opportunities for Payload Specialists will be made available whenever possible on a reimbursable basis to all classes of Space Shuttle major payload customers, including foreign and domestic commercial customers, international cooperative partners, the scientific and applications community and the Department of Defense.

On the first four flights of the Shuttle, there were two crew merpbers aboard, the commander and pilot. The fifth carried four, adding two Mission Specialists, who helped in deploying two commercial communication satellites. In the future. Mission Specialists, who are experts in extravehicular activity, operation of the Remote Manipulator System and payload support systems, will be joined by Payload Specialists on specific missions. They will be added to selected flights to provide detailed, on-the-spot expertise concerning payloads or scientific experiments. They will most often be scientists, with special skills to operate a scientific experiment, or a specialist proposed by a Shuttle customer trained in the critical aspects of deploying and operating a satellite.

Proposed Payload Specialists will undergo a short training period in preparation for flight. NASA will retain final selection authority to insure that they are fully qualified and can work as part of the flight crew.

VOYAGER 2 PRESSES ON

The Voyager 2 spacecraft has now travelled about one tenth of the distance it must cover for its encounter with the planet Uranus, projected for 24 January 1986. In the five years since its launch on 20 August 1978, the probe has travelled 3000 million km and is now 1700 million km from Earth. Most of the science instruments are functioning well after more than 40,000 hours of operating time.

Sixty-seven of the original 104 kg of propellant remain to be used for attitude control and trajectory correction. The two radioisotope thermoelectric generators are furnishing 422 watts of electrical power, which is 92 watts more than the requirement. The two areas of concern are one scan platform actuator which is showing signs of wear and the radio receiver which has reduced tracking capability. Neither of these problems is expected to seriously affect the future encounter with Uranus. Mission controllers at NASA's Jet Propulsion Laboratory in California are in daily contact with the spacecraft as its science instruments monitor the interplanetary environment. One-way radio time from Voyager 2 to Earth is now 90 minutes.

Voyager now has sufficient velocity to ultimately escape from the Solar System even though it has yet to fly by Uranus in 1986 and possibly Neptune in 1989. With a heliocentric velocity of 19.9 km per second (44,600 miles pfer hour), it has the distinction of being the second fastest object made by man. Its sister ship, Voyager 1, is travelling slightly faster. In its epic journey thus far. Voyager 2 has obtained approximately 32,000 images of Jupiter and Saturn with their rings and 13 major satellites. Planning is already underway for photographing Uranus with its rings and five satellites in 1986.

IMPROVED SHUTTLE BOOSTERS

A high performance booster motor for the Space Shuttle was test fired for the first time last October. The motor has been redesigned to increase the initial thrust of the Shuttle at liftoff, allowing the reusable spacecraft to carry more payload.

According to Frank Adams, deputy manager of the Solid Rocket Booster Project Office at NASA's Marshall Space Flight Center, the thrust increase was achieved in several ways. "To the casual observer, the motor will look the same as those we are presently using. However, we have reduced the size of the 'throat' and increased the length of the motor's exit cone. We have also increased the burn surface of the propellant by removing some of the inhibitor used at the ends of the four centre motor segments," said Adams. "These changes will give the motor a higher specific impulse which increases its performance and thrust."

The higher thrust motors will be used for the first time on the eighth Shuttle flight, now scheduled for mid-1983. The two motors will provide an additional 4 per cent thrust over the motors currently in use which deliver about 2.8 million pounds of thrust (12.5 MN) at liftoff.

Two giant Solid Rocket Boosters provide approximately 75 per cent of the Shuttle's power for liftoff from the launch pad and during the first two minutes of flight. After their propellant has burned out, the boosters separate from the Shuttle and parachute into the ocean where they are recovered and returned to Kennedy Space Center. They are then refurbished and reused on subsequent Shuttle missions.

MARS/MOON MISSION STUDIES

RCA Astro-Electronics, builders of the Tiros and some of the Explorer satellites, have been asked by the Jet Propulsion Laboratory in California to study the feasibility of converting their spacecraft for Mars and Lunar-orbiting missions. The two satellite concepts are:

• The Mars Geoscience Orbiter (MGO), which would operate for one year in a low polar orbit over Mars and carry a gamma-ray spectrometer, multi-spectral mapper, magnetometer and a radar altimeter.

• The Lunar Geoscience Orbiter (LGO), which would operate for one Earth year in a low polar orbit over the Moon. It would carry the same complement of instruments as the MGO, plus an X-ray spectrometer and electron reflectometer.