UARS:

UARS was launched onboard Space Shuttle Discovery on September 12, 1991, as part of the STS-48 mission.

To read about Discovery and her sisters – from birth, processing, every single mission, through to retirement, click here for the links:
http://forum.nasaspaceflight.com/index.php?topic=25837.0

It was deployed from Discovery’s Payload Bay, via her Shuttle Remote Manipulator System (SRMS), on Flight Day 3 of the mission (September 15). Discovery then returned home on September 18, landing at Edwards Air Force Base’s Runway 22.

The satellite was the first multi-instrumented spacecraft to observe numerous chemical components of the atmosphere for better understanding of photochemistry. UARS data marked the beginning of many long-term records for key chemicals in the atmosphere.

The satellite also provided key data on the amount of light that comes from the sun at ultraviolet and visible wavelengths.

UARS – which is 35 feet long, 15 feet in diameter, and weighs 13,000 pounds – ceased its productive scientific life in 2005, whilst on its orbit at an altitude of 375 miles with an orbital inclination of 57 degrees. It was originally designed to operate for only three years.

Now out of fuel, the satellite has been dropping out of orbit, and is expected to re-enter around September 23. The problem is, NASA aren’t sure where it will re-enter until next week, which has gained media attention, given experts believe at least 26 large pieces of the satellite are expected to survive re-entry.

All NASA know at this point is the satellite will re-enter somewhere between the latitudes of northern Canada and southern South America. While the hope – via probability – is any surviving pieces of UARS will impact over water, it highlights the need to work a level of mitigation into other returning objects from space.

NASA Meeting:

The timing of the UARS re-entry comes shortly after NASA’s FOIG team held a Special Safety Topic review into the hazards posed by space hardware fragmentation during re-entry, with the aim to apply mitigation to any potential risks from hardware breaking up and surviving entry – in turn threatening human life on the ground.

“As we progress forward with future programs, we should keep in mind that in systems engineering the definition of a System Life Cycle includes not just deployment and operation but also retirement and disposal,” a presentation from the meeting (available on L2) noted.

Several examples of hardware entering and surviving the extreme heat and aerodynamic stresses – which usually destroys returning hardware – are cited, starting with Apollo 13′s Lunar Module in April, 1970.

“The Aquarius LEM re-entered Earth’s atmosphere after having served as a lifeboat for the Apollo 13 crew. Mounted on the LEM descent stage, was a SNAP-27 (System For Nuclear Auxiliary Power) RTG (Radioisotope Thermoelectric Generator) which contained 8.3 lbs (3.9 kg) of Plutonium-238,” noted the presentation.

“Re-entry was at 122 km above the South Pacific Ocean near the Fiji Islands. High and low altitude atmospheric sampling in the area indicated there was no release of plutonium, so the graphite fuel cask is assumed to have survived re-entry and now resides on the bottom of the Tonga Trench in 6 to 9 km of water.”

The second example overviewed also had a nuclear element of concern, as the Soviet COSMOS-954 satellite failed to safe itself prior to returning back to Earth in 1978.

“COSMOS – A Soviet surveillance satellite that used a nuclear reactor for power (~50 kg of Uranium-235). By design, at the end of the satellite’s life, the reactor was supposed to separate and be boosted to a high parking orbit.

“COSMOS-954′s reactor failed to separate and when it re-entered, pieces of the satellite fell over a sparsely populated section of the North West Territories in Canada. 12 large pieces were recovered. Some were highly radioactive (less than 1 percent of the fuel was recovered).”

The presentation also notes that in 1983, COSMOS-1402 landed in the Indian Ocean, while in 1988, COSMOS-1900 landed in the Atlantic Ocean.

The third example shown related to the US station Skylab, which had originally hoped for an orbital reboost from an early space shuttle mission, prior to an eventful re-entry in July of 1979, which resulted in large pieces of hardware surviving.

“Increased solar activity, along with shuttle delays prevented any possibility of a reboost of the 90.6 ton space station. JSC (Johnson Space Center) controllers commanded Skylab into a tumble, hoping this would increase the amount of disintegration upon re-entry.

“Large chunks of debris were spread over a 100 mile long strip of land near Perth, Australia.”

The Russian’s own space station also suffered the fate of re-entry, as MIR saw its life ended in 2001. However, while a lot of pieces of the station survived, all the hardware followed a pre-planned disposal corridor over the southern Pacific Ocean.

“After a 15 year on-orbit life, the 135 ton orbital complex, was intentionally de-orbited by firing the thrusters of the attached Progress M1-5,” added the presentation’s overview.

“Entry was East of Australia, over the southern Pacific Ocean. Approximately 1,500 pieces of debris weighing 50 tons may have survived, including pieces as heavy as a small car.”

Other examples include an incident during Columbia’s STS-75 mission, when the Tethered Satellite System (TSS) was to be deployed to a distance of 12 miles to place the TSS into the rarefied electrically charged layer of the atmosphere known as the ionosphere.

As described in Chris Gebhardt’s superb overview of Columbia’s service and missions, it was hoped that the TSS would generate high voltage and electrical currents as it moved through the ionosphere and across the magnetic field lines of Earth.

This, in turn, would allow scientists to learn more about the electrodynamics of a conducting tether system and to deepen understanding of physical processes in the near-Earth space environment.

Deployment of the TSS proved successful at first. But just before the TSS reached full deployment, the tether snapped and the TSS was lost. It remained in orbit for several weeks before finally re-entering Earth’s atmosphere.

“During the STS-75 mission, with the TSS at 19.6 km (of a planned 20 km deployment), the tether broke due to a break down in insulation, short and subsequent melting of the cable,” added the presentation.

“At this point the 518 kg TSS became a free flying satellite (trailing a very long tail). While the satellite and tether did not pose a hazard to the ground, there was pre-flight concern that should the tether break, it could pose a re-contact risk to the orbiter.

“Side Note: Post break, MOD personnel sent a number of commands to the now free flyer, initially via the PI to save consumables and latter via ESTL (by building discrete commands).”

Tragically, Columbia herself provided the next example, after she – and her crew – were lost over east Texas during the ill-fated entry at the end of her STS-107 mission. Her loss resulted in additional work on computer models related to the mitigation of public risk for spacecraft debris.

“In the vicinity that debris fell, there are an average of 85 inhabitants per square mile. In the aftermath of the accident, NASA pursued the development of computer tools to predict the survivability of spacecraft debris during re-entry to help assess public risk. Entry paths were modified to mitigate the risk posed by the over flight of densely populated areas.”

The final example cited was USA-193 – also known as NRO launch 21 – was a military spy satellite launched on December 14, 2006 – the first launch of the then newly formed United Launch Alliance (ULA), via a Delta II launch vehicle.

Unfortunately, the satellite malfunctioned shortly after deployment,and was intentionally destroyed 14 months later on February 21, 2008, by a modified SM-3 missile fired from the warship USS Lake Erie, stationed west of Hawaii.

“Shortly after launch, all communication with a 5000 lbs, classified, US experimental radar reconnaissance satellite, was lost. The decision was made to destroy the satellite to prevent larger pieces from reaching the ground,” the presentation noted.

“The primary reported concern was contamination should the onboard hydrazine tank survive to the ground. A secondary concern was the classified nature of any hardware that did make it to the ground.

“A SM-3 missile was fired from the USS Lake Erie in the Pacific Ocean. The impact caused the satellite to break into more than 80 pieces, which at its orbital altitude (150 nmiles) , was expected to have a short lifetime (24-48 hours for most debris, with some not entering for 40 days).”

As NASA aim to control debris both in space and from surviving entry, the presentation noted that the International Space Station (ISS) has provided additional insights – from the standpoint of what they jettison from the orbital outpost.

“As the ISS program progressed, it became apparent that there needed to exist a standard policy for the jettison of hardware. Reasons for jettison could include: Safety issue for return (contamination, material properties, etc.). On-orbit stowage return manifest. EVA timeline savings. Hardware is designed to be jettison (ex. micro-sat).

As noted in flight rules (FR B4-104) for jettisoning hardware, “Whenever possible, hardware will be jettisoned from the ISS in a retrograde direction.” This allows controllers on the ground to analyze the expected relative motion, and ensure the jettisoned item cannot pose a collision hazard to ISS. USSTRATCOM are notified by NASA – and if available, a state vector provided.

Click here for ISS Articles: http://www.nasaspaceflight.com/tag/iss/

NASA managers now find themselves having to be vigilant to provide mitigation of hardware risks, with several current vehicles designed to end their lives in the fire of re-entry. Managers will also have to apply such planning for future vehicles, not least the fleet of new vehicles, such as SpaceX’s Dragon, and NASA’s own Orion (MPCV).

“ATV (ESA), HTV (JAXA) and Progress (Russia): End of mission disposal is via atmospheric re-entry. Soyuz (Russia): While the Descent Module re-enters and is recovered, support hardware is jettisoned (ex. Orbital Module and Instrumentation and Science Module),” added the presentation.

“COTS (Commercial) Visiting Vehicles (Future): Support hardware is jettisoned (ex. Dragon Service Module). Orion MPCV Hardware (Future). Support hardware is jettisoned (ex. Orion Service Module). Earth orbit tests of future asteroid/lunar hardware.”

According to the Special Safety Topic meeting’s findings, the key to providing additional mitigation against risks to the public will be found via improving computer models on how hardware is expected to disintegrate during entry.

“Improving re-entry fragmentation models can help ensure that planned (or contingency) disposal of on orbit hardware does not pose a hazard to the public. For first entry of new program (unproven) hardware, tracking and interception helps to ensure a safe trajectory and provide confirmation of the above models.”

On the whole, no risks are associated with re-entering vehicles, given the tight pre-planned disposal corridors. The mitigation – however – will provide a safety net for those vehicles which may suffer an issue and an uncontrolled re-entry.

(Images: Via the cited presentation – available on L2, plus ESA and NASA TV.)

(L2 is – as it has been for the past several years – providing full exclusive future vehicle coverage, available no where else on the internet. To join L2, click here: http://www.nasaspaceflight.com/l2/)

No related posts.

An amazing amount of work has taken place with the tanks that are constructed at Lockheed Martin’s Michoud Assembly Facility (MAF) in New Orleans, successfully rising to the challenge of reducing the threat of debris – mainly in the form of foam – shedding from the tanks during ascent, due to the potential of damaging impacts with the orbiter’s Thermal Protection System (TPS).

ET-129, which flew with Endeavour during STS-126′s launch, was the cleanest tank yet, with only a few areas of minor foam loss.

“(4) observations elevated as Post Flight Assessment Reports (PFARs) and assessed as IFA candidates. No new failure modes identified. No constraints or corrective actions required for STS-119/ET-127. No IFAs recommended for STS-126/ET-129.”

All areas of foam loss were deemed as “understood” and relate to either cryopumping during ascent – a known condition, or small areas of manufacturing damage suffered due to “high traffic” of engineers working in certain areas of the tank. Corrective actions have been noted on latter, via the FRR documentation.

However, STS-126 did suffer one debris threat during early first stage flight.

Although ice is a debris threat from the ET, the STS-126 event originated from Endeavour herself, according to ascent imagery. However, the debris failed to impact the vehicle.

“During STS-126, at approximately 26.7 seconds, debris was observed to liberate between the LH2 T-0 umbilical and port OMS pod,” noted one of 43 FRR presentations, available on L2.

“Imagery analysis concluded that liberated ice measured approximately 11.5” x 2”,” noted the presentation on the size of the ice debris. “Imagery and Debris Team trajectory analysis confirmed no contact with the Orbiter.”

The T-0 umbilicals – located on each side of the orbiter – and mated to the orbiter via retractable plates in the Tail Service Masts (TSMs), which can be seen either side of the orbiter’s aft.

As the name suggests, the T-0 umbilcals are retracted just as the vehicle is lift-offs, and it is thought the ice developed on the carrier plate of the LH2 umbilical during tanking. The ice remained with the orbiter before liberating 26 seconds later.

“KSC led resolution team to determine root cause for STS-126 T-0 ice formation,” noted the FRR presentation. “Decision to perform full analysis to assess risk for future flights over range of masses and release times.”

Engineers studied video taken of the T-0 umbilical area during lift-off, and included historical footage all the way back to STS-51L, and reviewed potential impact threats to several areas of the vehicle. Image left from STS-126′s 330mb engineering launch video on L2 - angle from inside the TSM during LH2 T-0 umbilical retraction.

“Produced impact conditions for Orbiter elements: Side Fuselage, OMS Pods, OMS Nozzle, Body Flap, Upper Wing, Elevon, and SSMEs (Space Shuttle Main Engines, plus RSRB (Reusable Solid Rocket Motors) and ET impacts.”

Work is still taking place on threat analysis, following checks of the pad’s GSE (Ground Support Equipment) on the Mobile Launch Platform (MLP), and on the umbilical connection area on Discovery.

“Purge test on MLP 1 LH2 Tail Service Mast (TSM) Umbilical Helium flow test completed,” noted the status of the investigation. “Inspection of T-0 Umbilical Carrier plate perimeter seal interface on OV-103 (Discovery) T-0 Plate completed.

“Debris Transport Analysis (DTA) of ice/frost release in work to characterize risk. Fault Tree Analysis and Block closure is in work. Assessing Ground Support Equipment hardware and process options to prevent ice/frost or have it liberate at/before T-0.”

Preventative actions for future flights will be the only outcome of the investigation, as opposed to being a threat for STS-119′s launch.

The only threat to launch at present relates to the Flow Control Valve (FCV) changeout, which is taking place over the next week.

While the changeout will be performed in time for launch, flight rationale for the spare valves on Discovery – and the LON (Launch On Need) orbiter Endeavour – is still being built.

This issue remains the one constraint for flight as per the SSP FRR last week.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. SRB Holddown posts undergoing redesign evaluation ahead of STS-119 Engineers will meet in the middle of January to push...

The Holddown Post (HDP) #3 Debris Containment System (DCS) failure has already led to an agreed redesign of the system, as reported by this site last week.

However, with STS-119 just five weeks away, the need for the modified solution to containing debris during the release of the four holddown posts (studs) on each booster has gained importance, following the findings of a Debris Risk Assessment study, which was created in late December – with refinements to the findings continuing until the end of this week.

“Objective: Provide assessment of risk to SSV (Space Shuttle Vehicle) from debris liberated by anomaly experienced on HDP#3 on STS-126,” opened the presentation on the assessment’s findings, available on L2.

An integrated team was assembled to carry out the study, which included the MSFC (Marshall Space Flight Center) Lift Off Debris Team, who provided lift off debris expertise and flow field information, along with a team specific to the Reusable Solid Rocket Motors (RSRM).

They were joined by the “USA Graybeards” – engineers that have been involved with Kennedy Space Center systems since the start of the shuttle program and in some cases as far back as the Apollo era. A number of these “graybeards” are currently helping Constellation engineers through their design issues with the Ares vehicles.

“Assignment: Provide a physics based credible and conservative (bounding) debris trajectory analysis that determines if a STS-126 type failed HDP creates debris that threatens the SSV at lift off,” the presentation continued. “Based on the analysis result, provide a quantitative risk assessment.”

Two categories of debris sources were considered, opening with debris from an unseated blast shield cover, and a spring in pieces of different sizes or whole spring – the latter being the largest liberation of debris from STS-126′s event, after it was later found in the north trench at Pad 39A. Plunger pieces of different sizes or whole, and non-metallic shims were also considered in this opening scenario.

The second category referenced debris sources from the RSRB Hold Down Post bore hole, such as plunger pieces and frangible nut pieces, among other items.

Several elements of the opening assessment findings were completed by mid December, such as a “successful TIM (Technical Interchange Meeting) with the Graybeard team, leading to both nominal and failed hold down post system physical characteristics and detailed kinematics explanation being completed, along with the identification of the local geometry near the hold down post.

Other items such as the effect of 2-RSRB plume interaction “needs to be defined to account for possible fluid dynamic mechanism to transport debris toward SSV,” which is set to be completed before the January 13 engineering summit meeting, which will be well ahead of the deadline of January 27 for the installation of the modified DCS on STS-119′s boosters.

The need for a solution to be certified in time for the next launch is made clear by the resulting findings of the assessment study, which shows debris from the holddown posts to be an impact threat on the vehicle.

“Plume driven debris: Debris starts inside the plume with enough initial upwards velocity to impact SSV. Debris is propelled down and out by the plume, impacts the MLP H/W (Hardware), rebounds with enough upwards velocity (no plume) to impact the SSV,” noted the presentation.

“RSRB plume edge impinges on the MLP causing a 90 deg plume flow turn and picking up debris (i.e., spring, non-metallic shim) from the HDP.

“This in turn imparts horizontal delta V to the debris and the plume and debris impact local H/W redirecting these another 90 deg toward the SSV…but now the plume energy diminishes but the debris has picked up enough velocity (approx 40fps) and might reach the SSV.

“RSRB plume excites spring causing it to break, and becomes debris for above scenario. Debris is propelled down and out, does a 180 deg turn via the flow-field, and has adequate upwards velocity (rebound plus plume-fountain effect) to impact SSV. Debris is propelled away from the vehicle downstream of the RSRB flame trench

“Other: Debris starts outside the plume with initial upwards velocity to impact SSV. Debris liberated from RSRB HDP bore hole is entrained into the plume boundary forcing the debris to impact the MLP H/W with enough energy to rebound and travel up to the SSV.”

The physical threat to the vehicle relates to either large pieces of debris – such as the large metal spring found in the north trench after STS-126 – or small sharp fragments of metal – such as tube lock clips – potentially impacting an OMS Pod, a SSME (Space Shuttle Main Engine), an aft Reaction Control System (RSC) “venier” thruster, or part of the vehicle’s TPS (Thermal Protection System).

An impact, such as one referenced at 40 foot per second, might not cause damage to the vehicle, as the vehicle is also racing off the pad.

However, engineers will assess the threat to the greatest detail to ensure a full understanding of the issue, should the certification of the modified DCS fail to be approved in time for STS-119.

That risk is also reduced by flight history, with only one other comparable event with the holddown post DCS occurring over the history of the shuttle program – that being in 1993 with STS-56 – which has no notes of vehicle damage being sustained.

With the full assessment study findings set to be completed – as early as this Friday – ahead of the engineering summit, and the expected certification of the modified DCS, STS-119 should be fully protected from the holddown post debris threat, thanks to expansive process that shuttle engineers carry out on every anomaly recorded on the previous mission.

L2 members: All documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.

Related posts:

1. SRB Holddown posts undergoing redesign evaluation ahead of STS-119 Engineers will meet in the middle of January to push...