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Stardust-next : Lessons Learned from a Comet Flyby Mission
The Stardust-NExT (New Exploration of Tempel) mission, a follow-on to the Stardust prime mission, successfully completed a flyby of comet Tempel-1 on 2/14/11. However there were many challenges along the way, most significantly low propellant margin and detection of the comet in imagery later than antici-pated. These challenges and their ramifications forced the project to respond with flexibility and ingenuity. As a result, the flyby at an altitude of 178 km was nearly flawless, accomplishing all its science objectives. Lessons learned on Stardust-NExT may have relevance to other spacecraft missions.
Preliminary analysis of cometary dust trails
Dust trails are observed in the orbits of some short-period comets. Large particles, having diameters in the submillimeter range and larger, are ejected by these comets into orbits close to that of the parent comet. By considering the effects of ejection and radiation forces, the spread of particles of different diameters along a parent comet's orbit, both ahead and behind the comet in mean anomaly were modeled. Using this model, the ages of the dust trail material associated with P/Tempel 2, P/Gunn, P/Encke, and P/Schwassmann-Wachmann 1 were estimated; they are found to consist of emissions occurring over a minimum of one to a few orbital periods. It also becomes possible to constrain the particle diameters in a trail segment forward of a comet's orbital position. Such a forward extension is observed in the Tempel 2 and Gunn dust trails, but not the Encke and S-W 1 dust trails. Relative particle sizes among these trails are discussed. The Tempel 2 dust trail is found to have an excess of particles with diameters greater than 1 mm.
The Tempel 2 dust trail
The IAS satellite's extensive observations of Comet Tempel 2 dust trail suggest that it is composed of particles of greater-than-1 mm diameter, whose velocities relative to the comet (assuming isotropic emission) are in the range of several m/sec. Excess color temperatures obtained relative to a blackbody indicate that either (1) the particles are large enough to support a temperature gradient over their surfaces, or (2) a small-particle population exists whose diameters are smaller than 100 A. If these small particles had not originated from the large particles, their acceleration to km/sec velocities by the gas outflow would have prevented their ejection into trail orbits.
Mission summary: Halley flyby/Tempel-2 rendezvous
A unique dual-comet flight opportunity exists in mid-1985 which includes flyby of the large and active comet Halley en route to rendezvous with second comet, Tempel-2. This mission will utilize ion propulsion at a modest performance level, based on proven technology. The Project is planned for FY81 start. Launch occurs in July 1985 via the Shuttle/IUS twin stage. Following IUS injection, the ion propulsion stage provides continuous thrust virtually throughout the 3-year flight until the Tempel-2 rendezvous in 1988. En route, a probe is deployed for encounter with Halley about 4 months after launch at a point 73 days before its perihelion. Rendezvous with Tempel-2 occurs about 60 days before the comet's perihelion during the summer of 1988 and continues for about 1 year. Earth will be in favorable relative positions for observing both the flyby and the rendezvous.
Comet Tempel 2: Orbit, ephemerides and error analysis
The dynamical behavior of comet Tempel 2 is investigated and the comet is found to be very well behaved and easily predictable. The nongravitational forces affecting the motion of this comet are the smallest of any comet that is affected by nongravitational forces. The sign and time history of these nongravitational forces imply (1) a direct rotation of the comet's nucleus and (2) the comet's ability to outgas has not changed substantially over its entire observational history. The well behaved dynamical motion of the comet, the well observed past apparitions, the small nongravitational forces and the excellent 1988 ground based observing conditions all contribute to relatively small position and velocity errors in 1988 -- the year of a proposed rendezvous space mission to this comet. To assist in planned ground based and earth orbital observations of this comet, ephemerides are given for the 1978-79, 1983-84 and 1988 apparitions.
Ground-based thermal IR images of Comet Tempel 2
The 10.8-micron images of Comet Tempel 2 obtained on the four days from September 21 to 24, 1988, indicate that the dust coma contributed about half of the nuclear pixel brightness. The nuclear condensation brightness exhibited a temporal variability slightly larger than observational uncertainty. The structure of the observed extended dust emission is interpretable as (1) a large grain tail primarily generated by cm-scaled particles, (2) the result of an outburst near 2.5-3.0 AU perihelion, and (3) a sunward emission of dust in a fanlike pattern.
A comet nucleus sample return mission
A comet nucleus sample return mission has been proposed for implementation near the end of this century. The objective of the mission is to collect a sample of undisturbed material from beneath the surface of an active comet and return it to earth in a minimally altered state. Potential targets include the short-period comets Encke, Tempel 2 and Wild 2. This paper defines such a mission and describes its requirements with regard to science, sampling, thermal protection and performance. It has been determined that with present launch capabilities, Solar Electric Propulsion (SEP) is an enabling technology for this mission and total program costs would be in the 700 million to 1 billion (FY '84) dollar range.
A thermal control approach for a solar electric propulsion thrust subsystem
A thrust subsystem thermal control design is defined for a Solar Electric Propulsion System (SEPS) proposed for the comet Halley Flyby/comet Tempel 2 rendezvous mission. A 114 node analytic model, developed and coded on the systems improved numerical differencing analyzer program, was employed. A description of the resulting thrust subsystem thermal design is presented as well as a description of the analytic model and comparisons of the predicted temperature profiles for various SEPS thermal configurations that were generated using this model. It was concluded that: (1) a BIMOD engine system thermal design can be autonomous; (2) an independent thrust subsystem thermal design is feasible; (3) the interface module electronics temperatures can be controlled by a passive radiator and supplementary heaters; (4) maintaining heat pipes above the freezing point would require an additional 322 watts of supplementary heating power for the situation where no thrusters are operating; (5) insulation is required around the power processors, and between the interface module and the avionics module, as well as in those areas which may be subjected to solar heating; and (6) insulation behind the heat pipe radiators is not necessary.
Nuclear electric propulsion missions
This paper reviews nuclear electric propulsion technology and missions. The science objectives and mission performance of the following five missions are presented: (1) Neptune orbiter, (2) Saturn ring rendezvous, (3) an asteroid sample return, (4) a comet sample return, and (5) an interstellar precursor mission. A short status of the reactor and thermal to electric conversion technologies is given as well as a brief discussion of ion thruster technology. A specific nuclear reactor power system concept is presented that produces 100 kWe and has a mass of about 2600 kg. Mission performance in terms of payload and flight time is presented for all five missions. Heliocentric trajectories are presented for the Neptune orbiter, Saturn ring rendezvous, and Comet Tempel 2 nucleus sample return missions.
The effects of argon in the bioenergetics of the hamster and the rat
Oxygen consumption was examined in hamsters and rats exposed to normoxic mixtures of argon at 1 atm. In fasted and nonfasted animals, no marked change in O2 utilization was detectable at 22 C. However, at 7 C a significant decrease in oxygen consumption was observed where the animals were exposed in argon. The data are interpreted in terms of the greater thermal conductivity of nitrogen. The study was prompted by conflicting reports on the metabolic effects of argon and helium.
Palomar and Table Mountain Observations of 9P/Tempel 1 during the Deep Impact Encounter: First Results
We present the first results of the Palomar Adaptive Optics observations taken during the Deep Impact encounter with 9P/Tempel 1 in July 2005. We have combined the Palomar near-IR imaging data with our visual wavelength images obtained simultaneously at JPL's Table Mountain Observatory to cover the total wavelength range from 0.4 to 2.3 micrometers in the B, V, R, I, J, H, and K filter bands, spanning the dates from 2005 July 03-07.We also include in our overall analysis images taken on the pre-encounter dates of June 1 and June 15, 2005. The broad wavelength range of our observations, along with high temporal resolution, near-IR sensitivity, and spatial resolution of our imaging, have enabled us to place constraints on the temperature of the impact flash and incandescent plume of greater than 700 K, and to provide mean dust velocities of order 197 +/- 16 m/s approximately 1.25 h after impact derived from our 1.64 micro observations. Our ejected dust mass estimates, as derived from our near-IR observations, are an order of magnitude less than those previously reported for visual wavelength observations.