Understanding the Engineering Behind Pixxel's Anand Satellite Launch Scrub
Understanding the space technology and aerospace engineering behind the recent Pixxel's Anand Satellite Launch Scrub.
Pixxel recently announced that their first satellite Anand won't be flying later this month. The company, founded in 2018, aims to launch a constellation of 24 satellites for daily global imaging of the Earth.
On 28th February'21, ISRO's PSLV-C51 will launch the Amazonia-1 satellite along with 18 co-passenger satellites. Pixxel's Anand satellite was one of the co-passenger satellites. On 23rd February, Pixxel's Twitter handle shared an image stating that it would not launch on the PSLV-C51 mission.
Anand Satellite Launch Scrub
Due to certain software issues that surfaced during the final satellite testing, we have decided not to proceed with our launch on the PSLV C51 mission scheduled for the 28th of this month. Given the time and effort that has gone into making the satellite, it did not make sense to rush a satellite to launch in which we do not have complete confidence at this time. We have thus decided to push our launch by a few weeks, reevaluate the satellite software, and test it rigorously over the next few weeks as we look for the next closest launch opportunity.
We would like to specially thank the ISRO, IN-SPACe and NSIL teams for the immense support they have been to us during this entire endeavour. From making testing facilities available to our satellite to providing support over the entire launch campaign, the help has been very encouraging to see. We wish the PSLV C51 mission the absolute best as it takes off on 28th Feb, 2021, albeit without us.
We'll keep you posted as we gear up for the launch.
The text in the image posted on their Twitter reads.
Pixxel's CEO, Awais Ahmed, also tweeted the same image while adding some information. According to him, "the HILS and the thermovac tests went beautifully without hiccups." Simultaneously, the company CTO Kshitij mentioned that they are currently aiming to get their SILS in line.
Understanding the Space Terms
To understand what went wrong, we need to know some of the terms used by Pixxel leaders.
SILS: SILS stands for the Software-In-Loop-Simulation. In simple terms, the satellite software is tested in a framework that imitates the environment. In this case, a dummy system is carrying out the test. It is not the actual hardware that will fly on the satellite.
HILS: Some of you may have guessed it. The 'H' here stands for Hardware. The rest of the abbreviation is the same as SILS. In HILS, the same software tested on a dummy system is now tested on the actual space hardware. The central computer, called the OBC, is connected to all other devices such as the sensors. Generally, the satellite is also fully integrated for this testing. A simulator makes the satellite believe that it is actually in Space. The software and the hardware are hence tested.
Thermovac: The SILS was a software test, while the HILS was a hardware cum software test. Thermovac is a little different. In thermovac, we place the integrated satellite into a vacuum chamber. The temperature inside the chamber is controlled to imitate the space environment. Therefore, here the satellite's thermal and vacuum properties are tested.
Understanding what when wrong
In an ideal scenario, SILS is followed by HILS. In contrast, the Thermovac can be performed before or after SILS. But the tweets of Pixxel indicate that the HILS and Thermovac completed nominally while SILS detected some issue.
There could be multiple reasons behind this. The primary point to understand is that we can perform these tests multiple times.
Therefore, I believe that a SILS test must be performed before the HILS and thermovac. Before the satellite's final integration with the launch vehicle, another SILS may have been tried. It is because SILS is one of the few tests which can be performed without any hardware.
This recent SILS test must have indicated some issue that was enough to scrub the launch.
All this is pretty normal in a space mission. Once a satellite is in space, there is very little that can be done to repair it. Therefore, it is necessary to test as much on the Earth. Let it fail on Earth so that it doesn't fail in Space.
Pixxel team has taken a courageous decision to scrub the Anand satellite launch. I hope they come back stronger and launch their satellite within a few months.
Edit: Awais and Kshitij confirmed the reasoning
Both Awais and Kshitij replied to my tweets and confirmed my theory. The SILS was performed before shipping the satellite to Sriharikota where some issue was observed. Due to a tight schedule, the Pixxel team decided to perform the hardware tests parallel to the SILS on a makeshift test jig. While this may sound as wrong. They made sure to appropriately write the test cases and success criteria for the test.
The test cases are various scenarios for which the test is performed.
Success criteria are pre-known conditions that, when achieved, mean that the test is passed.
CG + MOI is a test to calculate the center of gravity and moment of inertia of the satellite.