The European Space Agency (ESA) continues to set an example for the rest of the spacefaring world with its 11th-hour debris mitigation plan for the MetOp Second Generation (SG) polar-orbiting weather satellites.
The plan entails increasing the capacity of each satellite’s fuel tank so that it can be guided to a controlled atmospheric re-entry soon after the end of its 7.5-year mission. This will help ensure that the satellites — the program consists of three successive pairs of two spacecraft — do not remain in polar low Earth orbit for years after their mission ends. In addition, the 4,000-kilogram spacecraft will be steered to re-enter over the vast Pacific Ocean, thereby minimizing the chance that any debris that survives the fiery plunge can cause any damage.
Unfortunately, the latest annual report by ESA’s Space Debris Office suggests that these kinds of measures are still the exception rather the rule, at least when it comes to low-orbiting satellites. According to the report, presented to the Inter-Agency Space Debris Coordination Committee (IADC), whose members represent the world’s top spacefaring nations, the percentage of low-orbiting satellites being retired in accordance with IADC debris-mitigation guidelines is depressingly low. One has to wonder why this continues to be the case given the fact that the IADC first adopted the guidelines in 2002, and its members have been aware of the space debris threat since well before then.
ESA’s MetOp SG measure, inserted late in the competitive phase of the program, is not without cost. Award of the prime contract has been delayed three months to give competitors Astrium Satellites and Thales Alenia Space time to incorporate the new design requirements into their final bids, which are now due in late November. The delay and the design modification will no doubt translate into a higher price tag for the system.
But ESA Director-General Jean-Jacques Dordain was spot on in saying it is a small price to pay to help keep MetOp SG’s particular orbital belt, which is popular for weather and other environmental monitoring spacecraft, free of potentially hazardous debris. Mr. Dordain likely is especially sensitive on such matters: ESA’s 8,000-kilogram Envisat environmental satellite failed without warning in a similar orbit in April 2012 and, with its bristling array of exposed observing instruments, will be a huge hazard for the next 100 or so years.
Envisat of course was designed and built before the IADC adopted its guidelines. With the possible recent exception of the GOCE satellite, now headed toward an uncontrolled re-entry that some portion of its hardware is expected to survive, ESA has generally been a model citizen in safely disposing of spacecraft whose missions have been completed.
The report from ESA’s Space Debris Office, meanwhile, suggests that nations need to be far more vigilant about satellite end-of-mission disposal. The report found that of 38 satellites being retired at between 600 and 1,400 kilometers in altitude, just two were positioned in such a way as to assure re-entry within 25 years, as specified by IADC guidelines. Another two are expected to re-enter in around 25 years, while the remainder are likely to remain in orbit for longer — much longer, in some cases.
Countries seem to be doing a better job of keeping that orbital zone clear of spent rocket hardware. Of 29 rocket bodies left there in 2010 and 2011, nine were positioned for re-entry in less than 25 years.
More encouraging is the situation in the geostationary orbit arc 36,000 kilometers above the equator, where most communications satellites operate. Of fourteen satellites retired there in 2012, the report said, nine were boosted into graveyard orbits in accordance with the guidelines — a marked improvement over practices prior to the early 2000s. Moreover, in four of the five cases where satellites were not boosted clear of the geostationary arc, the owners at least made an attempt to do so.
Only one, Indonesia’s Cakrawarta 1, launched in 1997, appears to have been abandoned.
Notably, Indonesia is not a member of the IADC, as is the case with a growing number of countries now active in space. Adherence to the IADC’s guidelines might be improved through expanded membership. But it also seems evident that current members aren’t doing enough to preserve the environment in low orbit, and this needs to change. ESA, with MetOp SG, is showing that it’s possible.
