SMART-1 Mission Extension Approved
15 February 2005On 10 February 2005 the ESA Science Programme Committee endorsed unanimously the proposed one-year extension of SMART-1, pushing back the mission end date from August 2005 to August 2006.
Implementation of the mission extension will be in two periods of 6 months that correspond to different orbital parameters and illumination conditions. During the first period, the southern survey study is to be completed and dedicated pointings made for multi-angle, stereo, and polar illumination studies.
In the second period, high-resolution coverage of the Moon on the equator and part of the northern hemisphere will take place due to the favourable illumination conditions. High resolution follow up observations of specific targets will also be made, as well as observations relevant for the preparation of future international lunar exploration missions (Lunar-A, Selene, Chandrayaan-1, Chang'E, LRO, Moonrise).
Between 10 January and 9 February 2005 the SMART-1 electric propulsion drive was not active. This allowed mission controllers to accurately determine the amount of fuel remaining, as well as ensure accurate planning for a mission extension, and obtain reconnaissance data from an orbit at 1000-4500 km lunar altitude.
All the instruments have been performing well from this orbit. There are some thermal effects on the remote sensing payload that need to be monitored, in particular at times when the MGA medium gain antenna is pointed towards Earth.
As the electric propulsion system is now active again, SMART-1 will spiral down to arrive at the lunar science orbit by the end of February. A second lunar commissioning of the instruments, after which the baseline science mission will start, will follow this.
Highlights of cruise results
Over 110 papers, including 23 refereed papers, relating to SMART-1 have been published in scientific literature. There is a large public interest, as indicated by the media response, articles and the web presence, that showed Europe-wide visibility for SMART-1 science and technology.
The cruise and lunar approach has permitted the demonstration of a number of technologies, such as spacecraft, navigation, operations, and instruments, which will be useful for future missions. The SMART-1 mission has now fulfilled its primary objective – to demonstrate the viability of Solar Electric Propulsion.
The D-CIXS X-ray spectrometer has demonstrated its performance on calibration targets, and has monitored the X-ray variability of binaries and AGNs during the cruise phase. It has observed the Earth and, in particular, has detected the fluorescence from Earth's atmosphere, with a transition from Argon at 3 keV.
Detection of the first lunar X-ray photons occurred in January 2005 with identification of some key elements signatures.
The XSM solar monitor has measured the temporal variations of the Sun in the spectral range from 1 to 10 keV, and has detected number of flares during the cruise, in particular showing the changes in the flare continuum and Fe line. It will continue to measure the Sun in lunar orbit in order to calibrate D-CIXS.
The SIR infrared spectrometer showed nominal performance when it measured the first near-IR space spectra of the Moon in the range 0.9-2.5 microns. It also measured, for comparison, Earth reference spectra affected by atmospheric absorption. The comparison between spectra from different areas on the Moon has demonstrated the ability of the instrument to distinguish the mineralogy of different lunar areas.
The AMIE camera made a number of Earth observations and these are being used for educational and outreach purposes, as well as to measure scenes of planetary interest in various colour filters - such as geological features, volcanic terrains, deserts, ice caps, atmospheric features.
Observations of the Moon took place at different distances and lunar phases to validate the instrument performances and exposure times. AMIE also obtained the first historical record of an Earth-Moon portrait during a lunar eclipse on 28 October 2004. It obtained the first west European view of the lunar far side and North Pole in November 2004, and has started to acquire close up images from the lunar surface.
Science expected from the nominal science mission (January and March-July 2005)
The nominal science mission will contain a comprehensive observation survey giving simple and homogeneous coverage of the Moon, using mostly nadir pointing, and targeting of a few identified features of interest for detailed studies.
Due to its small, 1 milli-radian, field-of-view (FOV) and telemetry limitations, the SIR spectrometer will only cover a few percent of the surface during the first 6 months. The SIR spectrometric and AMIE colour measurements are done optimally near noon-midnight conditions (within ± 30°), which is possible only during an epoch of 2 months every 6 months.
For the first six months, the incident solar X-ray flux is expected to be sufficiently strong to derive a fluorescence map of the southern hemisphere for Mg, Si, and Al for a minimum surface coverage of 50% with an effective resolution of 60 km and sufficient sensitivity.
In high-resolution colour mode, it is expected that AMIE will cover a third of the lunar surface due to illumination and telemetry constraints. Completion of this survey will probably occur in April 2005 after a 2 month epoch of noon-midnight illumination conditions.
Rationale for extension
The SMART-1 extension of 1 year will provide opportunities:
- To extend the global coverage compared to the nominal 6 months mission, where good illumination conditions for IR spectrometry, X-ray sensitivity and quantitative colour radiometry will be encountered only for 25% of the time
- To make use of the new orbit (3000 km apolune instead of original 10 000 km) to map both southern and northern hemispheres at high resolution, and not only the southern hemisphere
- The new orbit is also more stable and requires less fuel for maintenance
- The extension increases the probability of solar flares events (especially in rising solar activity) for very sensitive D-CIXS scans providing high resolution maps of Fe and rare elements in addition to Mg, Si, Al
- The extension gives the possibility to perform detailed studies of areas of interest by performing stereo measurements for deriving topography, multi-angle observations for studying the photometric function and therefore the local regolith texture
- An extension allows to perform dedicated programmes to prepare future international lunar missions (seasonal illumination maps at high resolution, mapping potential landing sites for future missions, including the South Pole Aitken Sample Return)
SMART-1 Project Manager
ESA/ESTEC - SCI-PD
Keplerlaan 1- 2200 AG Noordwijk, The Netherlands
Bernard H. Foing
SMART-1 Project Scientist
ESA/ESTEC - SCI-SR
Keplerlaan 1- 2200 AG Noordwijk, The Netherlands