In its latest test of readiness for space, ESA’s Hera spacecraft for planetary defence is being operated for around three weeks in hard vacuum, while being subjected to the same temperature profiles it will experience during its journey to the Didymos binary asteroid system.
The 1.6 × 1.6 × 1.7 m spacecraft was slid inside the 4.5-m diameter, 11.8-m long Phenix thermal vacuum chamber at ESA’s ESTEC Test Centre in the Netherlands.
“You’re always a bit nervous when your baby gets moved about,” remarks Ian Carnelli, overseeing Hera for ESA. “Right now it’s being shut into a dark airless box for weeks on end, but we have confidence it will perform well.”
Hera can be seen receded into the rectangular ‘thermal tent’ within Phenix. The six copper walls of this internal box can be heated up to 100°C or cooled via piped liquid nitrogen down to –190°C, all independently from each other.
Then, after the main door of the stainless steel Phenix chamber was slid shut, the air within the chamber was pumped out during a lengthy 20 hours process down to approximately one billionth of outside atmospheric pressure. This will allow the Hera team from ESA, European Test Services operating the Test Centre and Hera manufacturer OHB to test the spacecraft’s thermal behaviour as the temperature changes around it.
Space is a place where it is possible to be hot and cold at the same time if one part of your spacecraft is in sunlight and another is in shade. And because there is no air, there is no conduction or convection to lose heat from your spacecraft. Instead thermal experts employ insulation and radiators to keep the body of a spacecraft within carefully chosen temperature limits. In general spacecraft electronics – just like their human makers – work best at room temperature.
“We already have detailed models of the spacecraft’s thermal behaviour, and this spacecraft-level thermal vacuum test lets us correlate these models with reality,” explains Hera’s Product Assurance and Safety manager, Heli Greus.
“More than 400 thermal sensors have been placed in and around Hera to give us precise knowledge of what is going on, and the test is being supervised on a 24/7 basis in case anything anomalous occurs. The spacecraft is now being put through a series of ‘cold plateaus’ and ‘hot plateaus’ representative of its mission, which will allow us to test the thermal limits of each specific unit aboard.”
Hera is Europe’s contribution to an international planetary defence experiment. Following the DART mission’s impact with the Dimorphos asteroid in 2022 – modifying its orbit and sending a plume of debris thousands of kilometres out into space – Hera will return to Dimorphos to perform a close-up survey of the crater left by DART. The mission will also measure Dimorphos’ mass and make-up, along with that of the larger Didymos asteroid that Dimorphos orbits around. Hera is due for launch in October 2024.
The ESTEC Test Centre in the Netherlands is the largest facility of its kind in Europe, providing a complete suite of equipment for all aspects of satellite testing under a single roof.