Ulysses - Abstract
Ulysses



David Borowsky


March 3, 1992

The goal of the Ulysses mission is to explore the Sun and its environment in unprecedented detail. This is a joint NASA/European Space Agency project, and it boasts many "firsts", including an out-of-ecliptic trajectory to allow the collection of data over the solar poles. The energy needed for such a path requires the craft uses Jupiter for a gravity-assisited plane change and velocity boost. This indirect path to the Sun will take time, and even though Ulysses was launched in October 1990, it will not complete its solar fly-over until September 1995. The route also allows for data gathering on the Solar environment between the planets, as well as the study of the Jovian system.

Previous studies of the Sun have only been done in the Ecliptic, and are thus a small glimpse of the dynamic solar environment. Although it will get no closer to the Sun than it was the day it was launched, the Ulysses spacecraft will provide a unique opportunity to explore the Heliosphere in total. It carries a 55 kg (121 lbm) instrument payload to collect data on the solar magnetic field, solar radiation such as radio and plasma waves and X-rays, and the solar wind, as well as cosmic radiation and dust entering the solar system. There are nine instruments:

  1. Solar Wind Plasma Experiment (SWPE);
  2. Solar Wind Ion Composition Spectrometer (SWICS), to detect heavy ions in the corona and provide an indirect way to measure its temperature;
  3. Heliospheric Instrument for Spectra, Composition, and Anisotropy at Low Energies (HI-SCALE), which will measure higher energy particles, such as those from solar flares;
  4. Energetic Particle Composition and Neutral Gas Experiment (EPAC/GAS), to examine medium energy particles;
  5. Cosmic Ray and Solar Charged Particle Investigation (COSPIN), for very high energy particles;
  6. Unified Radio and Plasma Wave Experiment (URAP) to measure high frequency radio waves and lower frequency plasma waves;
  7. Solar X-ray/Cosmic Gamma Ray Bursts Experiment (SCGRB);
  8. Magnetic Field Flux-Gate/Vector Helium Magnetometers (FGM/VHM), to study the solar magnetic field;
  9. Cosmic Dust Experiment (DUST).
In addition, the radio transmitter will be used to send radio waves into space at two different frequencies. These will allow a measurement of coronal particle densities and velocities when received on Earth. It is also hoped that the instruments will provide the first evidence for gravity waves, which are produced in violent cosmic interactions and are predicted to exist by Relativity theory.

These instruments are supported by an array of antennas. The main communication device is a 1.65 m (5.4 ft) diameter parabolic high gain antenna. There are also a 72.5 m (238 ft) dipole antenna; a 5.6 m (18.2 ft) radial antenna carrying experimental sensors, the SCGRB and the FGM/VHM; and a 7.5 m (24.3 ft) axial antenna for the URAP. All systems are joined to a 3.2 x 3.3 x 2.1 m (10.5 x 10.8 x 6.9 ft) main bus, which houses all the electronic systems and the hydrazine Reaction Control Sytem (RCS). Total craft mass is 367 kg (809 lbm).

Included in this mass is the Radioisotope Thermoelectric Generator power source, built by the U.S. The RTG runs on 10.75 kg (23.7 lbm) of Plutonium-238 dioxide and provides a maximum output of 283 Watts. The RTG caused some controversy over its safety and environmental impact, but it was the only feasible power plant option. All the instruments will be active continuously for almost 5 years, and current solar array technology does not have the capability to provide enough power at the distance of Jupiter. Arrays would also be severely degraded by the Jovian environment. The system had also been launched before without incident.

Ulysses' trajectory required the craft have as large a velocity as possible heading towards Jupiter. After going through eight different launch vehicle configurations during the 80's, it was launch by Shuttle and used both Inertial Upper Stage and Payload Assist Module-Shuttle (IUS/PAM-S) stages to orient and propel it. This was the first use of this upper stage configuration. The pointing for the flyby required the most precise orbiter/payload aligning of the Shuttle program. Ulysses had to hit a 100 mile wide "trajectory corridor" 500 million miles away for the correct plane change and solar trajectory. Dick Richards, Mission Commander for Discovery, called it a "360 nm hole in one".

The Ulysses misssion was set to launch in October 1990 on Discovery/STS-41. The launch window was the shortest ever for the Shuttle program, opening on the 5th and closing on the 23rd. If the launch was postponed for two consecutive days, a 48 hour hold would be needed to rest the crew. Missing the October window would cause a 13 month delay for the next opportunity.

The window on the 5th opened at 7:35 EDT, lasting 2 hr 18 min. Processing delays forced the launch to go on the second day of the window, starting again at 7:35 EDT but lasting 2 hr 35 min. Liftoff occurred from pad 39B at 7:47:06 EDT on the 6th. Ascent was a direct insertion profile, putting the shuttle on a 156 x 39 nm orbit with i = 28.5 deg.

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