Life past the leak for ESA’s CryoSat

On 21 November 2023, ESA’s CryoSat satellite tv for pc swapped to its back-up propulsion system after a gas leak threatened to deliver the mission to an finish in 2025.

The swap has the potential to increase the lifetime of the satellite tv for pc by as a lot as 5 to 10 years. However the back-up thrusters had by no means been used earlier than.

If one thing had broken them throughout CryoSat’s 13 years in orbit, there was a small likelihood that the mission would come to an instantaneous finish after the swap.

What’s CryoSat?

CryoSat is ESA’s satellite tv for pc devoted to measuring the thickness of polar sea ice and monitoring adjustments within the ice sheets that blanket Greenland and Antarctica.

The mission was designed to final roughly 5 years. It has now spent over 13 years in orbit.

“Since 2010, CryoSat has used its Artificial Radar Altimeter (SAR) to watch land and sea ice all over the place on Earth to assist scientists display the necessary function ice performs in regulating local weather and being affected by international warming,” says Tommaso Parrinello, CryoSat Mission Supervisor.

“CryoSat is a present that retains on giving. Its thirteen-year local weather document of worldwide ice and sea ranges is unparalleled, and lengthy might it proceed.”

Current mission highlights embrace the primary ever year-round map of Arctic Sea ice and our most correct estimates but for the ice quantity misplaced by Earth’s glaciers and polar ice sheets. These knowledge are essential to tell local weather experiences and coverage makers.

CryoSat’s knowledge are additionally shaping the design of recent ice-monitoring satellites, such because the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) mission.

What was the issue with CryoSat?

In an effort to make ultra-precise measurements of Earth or the cosmos, most satellites conduct common manoeuvres to maintain them within the good orbit.

CryoSat makes use of compressed nitrogen to manoeuvre in house. The gasoline is saved at excessive stress in a gas tank and carried by means of a collection of pipes and valves to thrusters. The thrusters launch the gasoline out into house, pushing or turning the satellite tv for pc in any commanded path.

Gas consumption was not anticipated to be a limiting issue for CryoSat. However in 2016, the operators flying CryoSat at ESA’s European House Operations Centre (ESOC) in Darmstadt, Germany, observed that the spacecraft was utilizing up its 37 kilograms of compressed nitrogen a lot sooner than anticipated.

As of November 2023, CryoSat has 13 kg of gas left – 13 kg much less gas left than it ought to have based mostly on using the thrusters for orbit upkeep manoeuvres and angle management.

When the gas tank drops beneath 5 kg, the satellite tv for pc will not have the ability to reliably management the path it factors or keep its orbit.

What precipitated the leak?

CryoSat’s nitrogen propellant is saved in a gas tank at excessive stress. A stress regulator converts the high-pressure air into a lot decrease stress to be used by the thrusters.

Along with the consultants on the satellite tv for pc’s producer, Airbus, the ESA group has pinpointed the situation of the leak to considered one of CryoSat’s smaller angle thrusters.

At first, the leak price was small, nevertheless it elevated over the primary few years and has reached a secure price that might nonetheless deliver the CryoSat mission to the top in 2025.

One rationalization for this may very well be {that a} small crack appeared someplace and grew to a sure dimension earlier than stopping. However it’s troublesome to diagnose this sort of drawback from the bottom, and it’s unimaginable to know for positive.

How did you save the satellite tv for pc?

CryoSat has a secondary, back-up propulsion system related to its gas tank.

On 21 November, at 10:45 CET, operators at ESOC initiated the swap to this back-up system, as CryoSat handed over Svalbard station on Spitzbergen Island and ESA’s Kiruna station in Sweden.

First, leaving the first thrusters related, they opened the principle valve to the back-up propulsion system for the primary time in CryoSat’s 13 years in house.

At ESOC in Germany, CryoSat’s spacecraft operations engineers and the group from Airbus monitored screens because the stress rose – each contained in the back-up propulsion system on CryoSat and within the management room on Earth.

The stress within the back-up system stabilised – indicating that it was not affected by any main problems with its personal – and the satellite tv for pc’s onboard pc was instructed to make use of the back-up thrusters as an alternative of the first thrusters that it has used since launch.

Simply earlier than CryoSat reached the top of its communication window with the stations within the Arctic, the principle valve to the first thrusters was closed to cease the movement of gasoline by means of the leak.

After which… silence.

CryoSat was left alone because it flew southbound over Africa, related to and utilizing its back-up thrusters for the primary time.

“CryoSat’s backup system is powerful and was more likely to work as meant,” says CryoSat Spacecraft Operations Supervisor, Jens Lerch. “And if there was an issue with it, in the course of the swap or at any level sooner or later, the satellite tv for pc is able to swapping again to its major system autonomously.”

“However we couldn’t know for positive. The back-up hasn’t been wanted in the course of the 13 years that CryoSat has been in house. Throughout this time, it may have suffered an analogous leak or been broken by one thing like a micrometeoroid – and we had no technique to take a look at it beforehand with out exposing us to the identical dangers we confronted at the moment.”

Fortunately, 25 minutes later, CryoSat rose above the horizon of the Troll floor station in Antarctica totally practical.

The subsequent day, 22 November, the flight management group at ESA performed an ‘orbital management manoeuvre’ to check the 2 bigger thrusters within the back-up system.

As no points had been discovered throughout or after the manoeuvre, CryoSat’s back-up thrusters at the moment are formally commissioned, and the satellite tv for pc is able to persevering with scientific actions to the top of the last decade and presumably past.

Maintain on, the leak was detected in 2016. Why wait till now to do one thing?

At any time since launch, CryoSat has had the power to swap to its back-up propulsion system if its onboard pc detected a sudden main subject with the first system.

However reacting to a sluggish leak represents a harder determination than reacting to a quick leak that have to be dealt with instantly and even autonomously by the satellite tv for pc.

CryoSat has gathered seven years of invaluable ice mapping knowledge between 2016 and 2023. If operators had switched to the back-up thrusters instantly, and a collection of impossible issues had occurred in the course of the reconfiguration, these knowledge would by no means have existed.

However the longer they waited, the extra gas leaked out into house, and the less further years they may acquire by making the swap.

21 November 2023 was chosen because the day that balanced these two components.

What subsequent?

The swap to CryoSat’s back-up thrusters was successful. However we don’t but know precisely how a lot this might lengthen the mission.

Solely by monitoring the gas reserves over the following few days and weeks will the CryoSat group know if there are any smaller leaks or points within the back-up system.

In the perfect case, this operation may show invaluable for humankind’s polar ice information.

CryoSat has been a key a part of what some have referred to as the “golden age of satellite tv for pc altimetry”. Amongst a powerful fleet, its radar altimeter is exclusive in having the ability to monitor ice and water ranges in each a part of the globe.

CRISTAL, CryoSat’s pure successor, just isn’t attributable to launch for an additional few years. The extension of CryoSat’s observations would bridge the hole and keep the longest unbroken document of adjusting international ice we have ever had.

In the meantime, a novel collaboration with NASA’s ice monitoring satellite tv for pc ICESat-2, which mixes the orbits of ICESat-2 and CryoSat to map snow on ice – a big reason behind uncertainty in our estimates – may enhance the accuracy of satellite tv for pc measurements of ice quantity but additional.

The findings might be instantly relevant additionally to future ice missions, together with CRISTAL.

With constant enhancements to CryoSat’s knowledge merchandise, which cowl not simply sea ice and land ice however polar oceans, coastal oceans and inland waters, ESA’s ice mission nonetheless has a lot to supply.