Ann P. Harch

The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros.

The NEAR-Shoemaker spacecraft was designed to provide a comprehensive characterization of the S-type asteroid 433 Eros (refs 1,2,3), an irregularly shaped body with approximate dimensions of 34 × 13 × 13 km. Following the completion of its year-long investigation, the mission was terminated with a controlled descent to its surface, in order to provide extremely high resolution images. Here we report the results of the descent on 12 February 2001, during which 70 images were obtained. The landing area is marked by a paucity of small craters and an abundance of ‘ejecta blocks’. The properties and distribution of ejecta blocks are discussed in a companion paper. The last sequence of images reveals a transition from the blocky surface to a smooth area, which we interpret as a ‘pond’. Properties of the ‘ponds’ are discussed in a second companion paper. The closest image, from an altitude of 129 m, shows the interior of a 100-m-diameter crater at 1-cm resolution.

An overview of the NEAR multispectral imager‐near‐infrared spectrometer investigation

The combined MSI-NIS investigation on NEAR consists of a Multi-Spectral Imager (MSI) and a Near-Infrared Spectrometer (NIS). MSI covers the spectral range from 0.4 to 1.1 μm in seven narrow passbands and one broad filter. MSI has a field of view of 2.25° by 2.90° and will achieve an image scale of about 3 m/pixel at the surface of Eros. NIS covers the spectral interval from 0.8 to 2.6 μm: the range between 0.804 and 1.506 μm is measured by a 32-element Germanium detector; a 32-element Indium-Gallium-Arsenide detector observes wavelengths between 1.348 and 2.600 μm. The instrument has a selectable field of view of either 0.38°×0.76° or 0.76°×0.76°. A spatial resolution of about 300 m (100 times coarser than MSI) can be achieved at Eros. A major goal of the MSI-NIS investigation is to determine the fundamental global properties of Eros, including spin state, size, and shape. Precise size and shape measurements are necessary to determine an accurate volume and thereby a mean density from mass measurements. MSI-NIS spectral data will be combined with abundance determinations of key rock-forming elements obtained by the X ray/gamma ray spectrometers (XGRS) to infer the distribution of minerals on Eros and constrain models of the asteroids geochemical evolution. On approach to Eros, a search will be made for satellites: objects as small as 12 m (some 100 times smaller than Idas Dactyl) could be detected.

Closing the uplink/downlink loop on the new Horizons Mission to Pluto

Commanding the payload on a spacecraft (“uplink” sequencing and command generation) and processing the instrument data returned (“downlink” data processing) are two primary functions of Science Operations on a mission. While vitally important, it is sometimes surprisingly difficult to connect data returned from a spacecraft to the corresponding commanding and sequencing information that created the data, especially when data processing is done via an automated science data pipeline and not via a manual process with humans in the loop. For a variety of reasons it is necessary to make such a connection and close this loop. Perhaps the most important reason is to ensure that all data asked for has arrived safely on the ground. This is especially critical when the mission must erase parts of the spacecraft memory to make room for new data; mistakes here can result in permanent loss of data. Additionally, there are often key pieces of information (such as intended observation target or certain instrument modes that are not included in housekeeping, etc.) that are known only at the time of commanding and never makes it down in the telemetry. Because missions like New Horizons strive to be frugal with how much telemetry is sent back to Earth, and the telemetry may not include unambiguous identifiers (like observation ids, etc.), connecting downlinked data with uplink command information in an automated way can require creative approaches and heuristics. In this paper, we describe how these challenges were overcome on the New Horizons Mission to Pluto. The system developed involves ingesting uplink information into a database and automatically correlating it with downlinked data products. This allows for more useful data searches and the ability to attach the original intent of each observation to the processed science data. Also a new data tracking tool is now being developed to help in planning data playback from the spacecraft and to ensure data is verified on the ground before being erased from spacecraft memory. The development of these tools and techniques have also uncovered powerful lessons-learned for future missions. At the early stages of the design of a missions dataflow, the allocation of a few more bytes of telemetry can go a long way toward making the uplink to downlink loop even easier to close on the ground, simplifying ground systems for future missions.

The CONTOUR remote imager and spectrometer (CRISP)

The CONTOUR Remote Imager and Spectrometer (CRISP) was a multi-function optical instrument developed for the Comet Nucleus Tour Spacecraft (CONTOUR). CONTOUR was a NASA Discovery class mission launched on July 3, 2002. This paper describes the design, fabrication, and testing of CRISP. Unfortunately, the CONTOUR spacecraft was destroyed on August 15, 2002 during the firing of the solid rocket motor that injected it into heliocentric orbit. CRISP was designed to return high quality science data from the solid nucleus at the heart of a comet. To do this during close range (order 100 km) and high speed (order 30 km/sec) flybys, it had an autonomous nucleus acquisition and tracking system which included a one axis tracking mirror mechanism and the ability to control the rotation of the spacecraft through a closed loop interface to the guidance and control system. The track loop was closed using the same images obtained for scientific investigations. A filter imaging system was designed to obtain multispectral and broadband images at resolutions as good as 4 meters per pixel. A near IR imaging spectrometer (or hyperspectral imager) was designed to obtain spectral signatures out to 2.5 micrometers with resolution of better than 100 meters spatially. Because of the high flyby speeds, CRISP was designed as a highly automated instrument with close coupling to the spacecraft, and was intended to obtain its best data in a very short period around closest approach. CRISP was accompanied in the CONTOUR science payload by CFI, the CONTOUR Forward Imager. CFI was optimized for highly sensitive observations at greater ranges. The two instruments provided highly complementary optical capabilities, while providing some degree of functional redundancy.