Emma M. Birath

Ultraviolet Discoveries at Asteroid (21) Lutetia by the Rosetta Alice Ultraviolet Spectrograph

The NASA Alice ultraviolet (UV) imaging spectrograph on board the ESA Rosetta comet orbiter successfully conducted a series of flyby observations of the large asteroid (21) Lutetia in the days surrounding Rosettas closest approach on 2010 July 10. Observations included a search for emission lines from gas, and spectral observations of the Lutetias surface reflectance. No emissions from gas around Lutetia were observed. Regarding the surface reflectance, we found that Lutetia has a distinctly different albedo and slope than both the asteroid (2867) Steins and Earths moon, the two most analogous objects studied in the far ultraviolet (FUV). Further, Lutetias ~10% geometric albedo near 1800 A is significantly lower than its 16%-19% albedo near 5500 A. Moreover, the FUV albedo shows a precipitous drop (to ~4%) between 1800 A and 1600 A, representing the strongest spectral absorption feature observed in Lutetias spectrum at any observed wavelength. Our surface reflectance fits are not unique but are consistent with a surface dominated by an EH5 chondrite, combined with multiple other possible surface constituents, including anorthite, water frost, and SO2 frost or a similar mid-UV absorber. The water frost identification is consistent with some data sets but inconsistent with others. The anorthite (feldspar) identification suggests that Lutetia is a differentiated body.

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.

Accommodating Navigation Uncertainties in the Pluto Encounter Sequence Design

The New Horizons encounter with the Pluto system was a historic achievement in planetary exploration. Launched on January 19, 2006, the spacecraft executed its close encounter with Pluto on July 14, 2015, acquiring the first-ever close up data of Pluto, its five known satellites, and the surrounding plasma and particle environment. During its 9½ year cruise, the spacecraft also conducted a flyby of an asteroid in 2006 and a Jupiter gravity assist in 2007 during which over 700 observations of Jupiter, the Galilean satellites, and the plasma and particle environment near Jupiter were acquired. Led by Principal Investigator Alan Stern, New Horizons was the first launch of NASA’s New Frontiers Program and the first mission to Pluto and the Kuiper Belt.