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STS-99
Part of STS
STS-99
STS-99
Credit: NASA
Deployed the 61 meter long STRM mast, a side-looking radar that digitally mapped the entire land surface of the Earth between latitudes 60 deg N and 54 deg S.

AKA: Endeavour;STRM. Launched: 2000-02-11. Returned: 2000-02-22. Number crew: 6 . Duration: 11.24 days.

On an extremely successful mission the space shuttle Endeavour deployed the 61 meter 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 maneuver 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.

NASA Official Mission Summary

STS-99
Mission: Shuttle Radar Topography Mission
Space Shuttle: Endeavour
Launch Pad: 39A
Launched: February 11, 2000, 12:43:40 p.m. EST
Landing Site: Kennedy Space Center, Florida
Landing: February 22, 2000, 6:22:23 p.m. EST
Runway: 33
Rollout Distance: 9,943 feet
Rollout Time: 62 seconds
Revolution: 181
Mission Duration: 11 days, 5 hours, 39 minutes 41 seconds
Orbit Altitude: 126 nautical miles
Orbit Inclination: 57 degrees
Miles Traveled: 4.1 million

Crew Members: Commander Kevin R. Kregel, Pilot Dominic L. Pudwill Gorie, Mission Specialists Janet L. Kavandi, Janice E. Voss, Mamoru Mohri and Gerhard P. J. Thiele.

Launch Highlights

STS-99 faced a series of launch delays and one scrub before launching successfully. The mission was originally scheduled to fly on Sept. 16, 1999. But in mid-August, the launch date was postponed until October because of wiring concerns throughout the shuttle fleet. With so much of Endeavour's wiring requiring inspection, the target date for launch was shifted to no earlier than Nov. 19. Shuttle managers later decided to preserve the option to launch either STS-99, or STS-103, the third Hubble Servicing Mission, first. It was decided in October that STS-103 would fly first, and the launch of STS-99 was set for Jan. 13, 2000. In December that date came under review, and a new launch date of no earlier than Jan. 31 was set.

The scheduled launch on Jan. 31, 2000, was scrubbed because of unacceptable weather conditions. However, late in the count, an anomaly occurred with the No. 2 enhanced master events controller (EMEC), which also would have prevented the launch on that day. The EMEC was removed and replaced and the launch rescheduled until 12:30 p.m. EST on Feb. 11. About three hours prior to the scheduled launch, an unexpected pressure drop was detected in hydraulic system 1. The pressure drop was determined to be the result of a normal sequence of prelaunch events. Discussions of the pressure drop resulted in a 13-minute, 40-second launch delay.

Mission Highlights

The Shuttle Radar Topography Mission mast was deployed successfully to its full length, and the antenna was turned to its operation position. After a successful checkout of the radar systems, mapping began at 12:31 a.m., less than 12 hours after launch. Crewmembers, split into two shifts so they could work around the clock, began mapping an area from 60 degrees north to 56 degrees south. Data was sent to Jet Propulsion Laboratory for analysis and early indications showed the data to be of excellent quality.

Mapping proceeded fairly smoothly, but during an attitude-hold period for payload mapping during the second day of flight, it was determined that orbiter propellant usage had doubled from 0.07 to 0.15 percent an hour. The increase was caused by a failure of the payload cold-gas thrust system that was used to offset the gravity gradient torque of the mast.

As a result of this failure, orbiter propellant was being used at a higher-than-planned rate to maintain the attitude of the vehicle. Measures to reduce the expenditure were evaluated and based on the analysis, enough propellant could be saved to complete the planned 9-day plus science mission.

The first of a series of "flycast" maneuvers during the mission was also made on the second day of flight. The flycast maneuver was designed to reduce strain on the almost-200-foot mast extending from Endeavour's cargo bay when adjustments to Endeavour's orbit were needed.

The orbiter, which flew tail-first during mapping operations, was moved to a nose-first attitude with the mast extending upward. A brief reaction control system pulse began the maneuver. The mast deflected slightly backwards, then rebounded forward. As it reached vertical, a stronger thrust was applied, arresting the mast's motion and increasing the orbiter's speed.

Radar data gathering concluded at 6:54 a.m. EST on the tenth day of flight after a final sweep across Australia. During 222 hours and 23 minutes of mapping, Endeavour's radar images filled 332 high density tapes and covered 99.98 percent of the planned mapping area -- land between 60 degrees north latitude and 56 degrees south latitude -- at least once and 94.6 percent of it twice. Only about 80,000 square miles in scattered areas remained unimaged, most of them in North America and most already well mapped by other methods. Enough data was gathered to fill the equivalent of 20,000 CD's.

Also aboard Endeavour was a student experiment called EarthKAM, which took 2,715 digital photos during the mission through an overhead flight-deck window. The NASA-sponsored program lets middle school students select photo targets and receive the images via the Internet. The pictures were used in classroom projects on earth science, geography, mathematics and space science. More than 75 middle schools around the world participated in the experiment, which set a record. On four previous flights combined, EarthKAM sent down a total of 2,018 images.

Statistics

STS-99 (97)

Milestones:

OPF -- 12/15/98; VAB -- 7/11/99; PAD -- 12/13/99

Payload:

SRTM, EarthKAM

Mission Objectives:

The Shuttle Radar Topography Mission (SRTM) was an international project spearheaded by the National Imagery and Mapping Agency and NASA, with participation of the German Aerospace Center DLR. Its objective was to obtain the most complete high-resolution digital topographic database of the Earth. SRTM consisted of a specially modified radar system that produced unrivaled 3-D images of the Earth's surface.

SRTM used C-band and X-band interferometric synthetic aperture radars (IFSARs) to acquire topographic data of the Earth's land mass between 60 deg N and 56 deg S. It produced digital topographic map products which met 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 was close to 1 trillion measurements of the Earth's topography. Besides contributing to the production of better maps, these measurements would lead to improved water drainage modeling, more realistic flight simulators, better locations for cell phone towers, and enhanced navigation safety.

Orbit: Altitude: 233 km / Inclination: 57 deg

Data Statistics

In addition, this mission offered 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.

Civilian Applications

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.

Military Applications

Flight simulators; logistical planning, air traffic management; missile and weapons guidance systems; and battlefield management, tactics.

Vehicle Data

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

The Mast

Made of carbon fiber reinforced plastic (CFRP), stainless steel, alpha titanium, and Invar, the mast was a truss structure that consisted of 87 cube-shaped sections called bays. Unique latches on the diagonal members of the truss allowed 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 housed the mast during launch and landing and also deployed and retracted the mast.

The mast was deployed and retracted by a motor-driven nut within the mast canister. This nut pulled the mast from its stowed configuration and allowed it to unfold like an accordion. An astronaut inside the Space Shuttle initiated the mast deployment. The mast also could have been deployed manually during an EVA using a hand-held motor if necessary.

The mast technology enabled the SRTM system to perform at the high precision necessary to achieve the desired mapping resolution. The mast supported a 360-kilogram antenna structure at its tip and carried 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 was connected to a pallet that in turn was bolted into the payload bay of the Space Shuttle. The system consisted of two antennas and the avionics that computed the position of the antenna.

Each antenna was made up of special panels that could transmit and receive radar signals. One antenna was the C-band antenna and could transmit and receive radar 5.6 centimeter wavelengths. The second antenna was the X-band antenna. This antenna could transmit and receive 3 centimeter radar wavelengths. 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, was removed to save weight.

History/Background

Attitude and Orbit Determination Avionics

In order to map the Earth's topography, SRTM researchers had to:

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 was flying

For example, if the Shuttle's height above sea level was known and its respective height above a mountain, then researchers could subtract to get the height of the mountain above sea level.

For the first part, researchers needed to know the Shuttle's height above sea level at all times. NASA needed to constantly measure the Shuttle position to an accuracy of 1 meter (about 3 feet).

For the second part of the formula, SRTM was using radar interferometry to measure the height of the Shuttle above the Earth's surface. One of the biggest challenges in making interferometry work was knowing the length and orientation of the mast at all times. Changes in its length and orientation could have a profound effect on the final height accuracy. Suppose the mast tip moved around by only 2 cm (a bit less than 1 inch) with respect to the Shuttle (this was something that was 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 expected 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 needed to constantly monitor the mast orientation and length. Part of this was measuring where the mast tip was relative to the Shuttle to better than 1 mm (about 4/100th of an inch). The other part was knowing how the Shuttle was oriented relative to the Earth to about 1 arcsec.

To keep track of the Shuttle's position, NASA made use of the Global Positioning System (GPS). Mission managers could 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 used a variety of optical sensors. A target tracker was used to follow a set of Light Emitting Diode (LED) targets which could be seen on the outboard radar antenna once the mast was fully deployed.

The target tracker also was used to monitor the antenna alignment. There were laptop computers on the Shuttle which displayed the antenna alignment (kind of a cross-hairs with a dot, representing the alignment error). The crew used these displays to guide adjust of some motors at the mast tip (the "milkstool") to remove any alignment errors so the radar could operate properly.

To get the most accurate measure of the mast length, SRTM managers used 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 worked 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 used one of the most precise star tracker and gyroscope packages ever built. The star tracker looked at the sky and compared what it saw with a star catalogue in its memory to get the attitude of the Shuttle.

EarthKAM In-Cabin

Prime: Kevin Kregel Backup: Dom Gorie

EarthKAM was a NASA-sponsored program that enabled middle school students to take photographs of the Earth from a camera aboard the Space Shuttle. During missions, students worked collectively and used 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 faced 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 was required for nominal operations.

The University of California at San Diego housed the EarthKAM Mission Operations Center (MOC). Most participating schools (or group of schools) establish a Student Mission Operation Center (SMOC) whose computers were connected to the Internet.

Before the mission, students selected a topic of interest, such as human settlement patterns, mountain ranges, or agricultural patterns. Then they defined investigations that were supported by the EarthKAM images.

During the mission, each SMOC submited a number of photo requests through specialized EarthKAM web pages. The requests were processed and uplinked to the EarthKAM ESC aboard the Shuttle.

After the ESC took the pictures, digital images were sent back to Earth and posted on the data system for the students to use in their investigations. For their final reports, students used these new images along with other relevant images from the full EarthKAM image set. Scientists and educators reviewed the original proposal and the final report to provide feedback to the students.

The EarthKAM program also was preparing to mount a camera aboard the International Space Station.

History/Background

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.


More at: STS-99.

Family: Manned spaceflight. People: Gorie, Kavandi, Kregel, Mohri, Thiele, Voss, Janice. Country: USA. Spacecraft: Endeavour. Projects: STS. Launch Sites: Cape Canaveral. Agency: NASA, NASA Houston.

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