On an extremely successful mission the space shuttle Endeavour deployed the 61 metre long STRM mast. This was a side-looking radar that digitally mapped with unprecedented accuracy the entire land surface of the Earth between latitudes 60 deg N and 54 deg S. Sponsors of the flight included the US National Imagery and Mapping Agency (NIMA), NASA, and the German and Italian space agencies. Some of the NIMA data would remain classified for exclusive use by the US Department of Defense.
The RSRM-71 solid rocket boosters separated at 17:45 GMT. The OMS engines fired in an OMS Assist manoeuvre during the ascent to orbit from 17:46 to 17:47 GMT. Main engine cut-off was at 17:52 GMT followed by separation of the ET-92 External Tank. At 18:19 GMT a 2 minute OMS-2 firing placed Endeavour in circular orbit, while the ET coasted to re-entry over the Pacific.
The SRTM mast was deployed successfully at 23:27 GMT on February 12. A failed thruster on the end of the mast caused some work-arounds but did not prevent successful completion of all planned mapping work. After some problems stowing the mast on February 21, Endeavour made a deorbit burn was at 22:25 GMT February 22 and landed at 23:22 GMT. The shuttle Endeavour was then towed to Orbiter Processing Facility Bay 2 to be prepared for the STS-97 mission.
Kevin R. Kregel (4), Mission Commander; Dominic L. Pudwill Gorie (2), Pilot; Janet L. Kavandi (2), Mission Specialist; Janice E. Voss (5), Mission Specialist; Mamoru Mohri (2), Mission Specialist (NASDA); Gerhard P.J. Thiele (1), Mission Specialist
OPF -- 12/15/98; VAB -- 7/11/99; PAD -- 12/13/99
The Shuttle Radar Topography Mission (SRTM) is an international project spearheaded by the National Imagery and Mapping Agency and NASA, with participation of the German Aerospace Center DLR. Its objective is to obtain the most complete high-resolution digital topographic database of the Earth. SRTM consists of a specially modified radar system that will fly onboard the space shuttle during its 11-day mission. This radar system will gather data that will produce unrivaled 3-D images of the Earth's surface.
SRTM uses C-band and X-band interferometric synthetic aperture radars (IFSARs) to acquire topographic data of Earth's land mass (between 60 deg N and 56 deg S). It produces digital topographic map products which meet Interferometric Terrain Height Data (ITHD)-2 specifications (30 meter x 30 meter spatial sampling with 16 meter absolute vertical height accuracy, 10 meter relative vertical height accuracy and 20 meter absolute horizontal circular accuracy).
The result of the Shuttle Radar Topography Mission could be close to 1 trillion measurements of the Earth's topography. Besides contributing to the production of better maps, these measurements could lead to improved water drainage modeling, more realistic flight simulators, better locations for cell phone towers, and enhanced navigation safety. The data brought home by Endeavour's crew was collected during more than 222 hours of around-the-clock radar mapping operations and is enough to fill more than 20,000 CDs. The information gathered on the STS-99 Shuttle Radar Topography Mission will be used to produce global maps more accurate than any available today.
Orbit: Altitude: 233 km / Inclination: 57 deg
In addition, this mission offers a number of applications for data products and science, including: geology, geophysics, earthquake research, volcano monitoring; hydrologic modeling; ecology; co-registration and terrain correction of remotely-acquired image data; atmospheric modeling; flood inundation modeling; urban planning; natural hazard consequence assessments; fire spread models; and transportation/infrastructure planning.
Enhanced ground collision avoidance systems for aircraft; civil engineering, land use planning, and disaster recovery efforts; and line-of-sight determination for communications, e.g., cellular telephones.
Flight simulators; logistical planning, air traffic management; missile and weapons guidance systems; and battlefield management, tactics.
Shuttle Liftoff Weight: 4,520,415 lbs. Orbiter/Payload Liftoff Weight: 256,560 lbs. Orbiter/Payload Landing Weight: 225,669 lbs.
Payload Weight: SRTM 14.5 tons
Software Version: OI-27
Space Shuttle Main Engines: SSME 1: 2052 SSME 2: 2044 SSME 3: 2047
External Tank: ET-92 ( Super Light Weight Tank)
SRB Set: BI-100/RSRM-71 SRTM Hardware--the Mast Payload Bay
Made of carbon fiber reinforced plastic (CFRP), stainless steel, alpha titanium, and Invar, the mast is a truss structure that consists of 87 cube-shaped sections called bays. Unique latches on the diagonal members of the truss allow the mechanism to deploy bay-by-bay out of the mast canister to a length of 60 meters (200 feet), about the length of five school buses. The canister houses the mast during launch and landing and also deploys and retracts the mast.
The mast will be deployed and retracted by a motor-driven nut within the mast canister. This nut will pull the mast from its stowed configuration and allow it to unfold like an accordion. An astronaut inside the Space Shuttle will initiate the mast deployment, which will take about 20 minutes. The mast also may be deployed manually during an EVA using a hand-held motor if necessary.
The mast technology enables the SRTM system to perform at the high precision necessary to achieve the desired mapping resolution. The mast supports a 360-kilogram antenna structure at its tip and carries 200 kilograms of stranded copper, coaxial, fiber optic cables, and thruster gas lines along its length.
The Shuttle Radar Topography Mission Mast
The Main Antenna
The main antenna is connected to a pallet that in turn is bolted into the payload bay of the Space Shuttle. The system consists of two antennas and the avionics that compute the position of the antenna.
Each antenna is made up of special panels that can transmit and receive radar signals. One antenna is the C-band antenna and can transmit and receive radar wavelengths that are 2.25 inches or 5.6 centimeters long. The second antenna is the X-band antenna. This antenna can transmit and receive radar wavelengths that are 1.2 inches or 3 centimeters long. Both wavelengths were used in the Spaceborne Imaging Radar C-band/X-SAR missions in 1994 for a variety of environmental studies. The L-band antenna, also used during SIR-C/X-SAR, has been removed to save weight.
Attitude and Orbit Determination Avionics
In order to map the Earth's topography, SRTM researchers will need to do two basic things:
1) Measure the distance from the Shuttle to some common reference, such as sea-level
2) Measure the distance from the Shuttle to the surface feature over which it is flying
For example, if the Shuttle's height above sea level is known and its respective height above a mountain, then researchers can subtract to get the height of the mountain above sea level.
For the first part, researchers need to know the Shuttle's height above sea level at all times. NASA will need to constantly measure the Shuttle position to an accuracy of 1 meter (about 3 feet).
For the second part of the formula, SRTM is using radar interferometry to measure the height of the Shuttle above the Earth's surface. One of the biggest challenges in making interferometry work is knowing the length and orientation of the mast at all times. Changes in its length and orientation can have a profound effect on the final height accuracy. Suppose the mast tip moves around by only 2 cm (a bit less than 1 inch) with respect to the Shuttle (this is something that is expected to happen during the mission, due to the astronauts moving around and Shuttle thrusters firing). That doesn't sound like much, but if not taken into account, it would result in a height error at the Earth's surface of 120 meters (almost 400 ft).
Researchers also expect changes in mast length of about 1 cm (about a half-inch) which if not detected would result in additional errors. Therefore, SRTM team members will need to constantly monitor the mast orientation and length. Part of this is measuring where the mast tip is relative to the Shuttle to better than 1 mm (about 4/100th of an inch). The other part is knowing how the Shuttle is oriented relative to the Earth to about 1 arcsec. An arcsecond is the angular size of a dime seen from a distance of 2 miles.
To keep track of the Shuttle's position, NASA will make use of the Global Positioning System (GPS). Mission managers do this by combining measurements taken by some specially designed GPS receivers being flown on the Shuttle with measurements taken by an international network of GPS ground receivers.
To measure the mast length and orientation, team members will use a variety of optical sensors. A target tracker will be used to follow a set of Light Emitting Diode (LED) targets which can be seen on the outboard radar antenna once the mast is fully deployed.
The target tracker also is used to monitor the antenna alignment. There are laptop computers on the Shuttle which display the antenna alignment (kind of a cross-hairs with a dot, representing the alignment error). The crew will use these displays to guide adjustment of some motors at the mast tip (the "milkstool") to remove any alignment errors so the radar can operate properly.
To get the most accurate measure of the mast length, SRTM managers will use a set of rangefinders, called Electronic Distance Measurement (EDM) units. To save time and money, the SRTM team decided to buy commercial surveying instruments and modify them for use in space. The rangefinders work by bouncing a beam of light off a special corner-cube reflector on the outboard antenna and measuring the time to determine the distance.
To measure the orientation of the Shuttle with respect to the Earth, mission managers will use one of the most precise star tracker and gyroscope packages ever built. The star tracker looks at the sky and compares what it sees with a star catalogue in its memory to get the attitude of the Shuttle.
Prime: Kevin Kregel Backup: Dom Gorie
EarthKAM is a NASA-sponsored program that enables middle school students to take photographs of the Earth from a camera aboard the Space Shuttle. During missions, students work collectively and use interactive web pages to target images and investigate the Earth from the unique perspective of space.
An electronic still camera (ESC) bracket-mounted to the overhead starboard window of the orbiter aft flight deck will face the nadir to observe various student-selected sites on Earth. Other than equipment setup, initial camera pointing, and possible camera lens changes, no crew intervention is required for nominal operations.
The University of California at San Diego houses the EarthKAM Mission Operations Center (MOC). Most participating schools (or group of schools) establish a Student Mission Operation Center (SMOC) whose computers are connected to the Internet.
Before the mission, students select a topic of interest, such as human settlement patterns, mountain ranges, or agricultural patterns. Then they define investigations that will be supported by the EarthKAM images.
During the mission, each SMOC submits a number of photo requests through specialized EarthKAM web pages. The requests are processed and uplinked to the EarthKAM ESC aboard the Shuttle.
After the ESC takes the pictures, digital images are sent back to Earth and posted on the data system for the students to use in their investigations. For their final reports, students use these new images along with other relevant images from the full EarthKAM image set. Scientists and educators review the original proposal and the final report to provide feedback to the students.
The EarthKAM program also is preparing to mount a camera aboard the International Space Station.
During the first four missions of EarthKAM, students took more than 2,000 high-resolution digital images of the Earth. These photographs included the Himalayas, clouds over the Pacific, volcanoes, and recent forest fires in Indonesia. References: 4 , 7 .