Satellites

Two Reasons Why the Humanity Star is Not a Complete Waste of Time

If you have not seen this, you should look at this web page that describes The Humanity Star.  It is basically a nearly spherical object that was launched into space in January of 2018.  It has 65 reflective surfaces that will reflect sunlight while it is in orbit. The general idea is that whenever it is in the sun, it will be so bright in the sky that you can see it.

Normal satellites can be seen in orbit around the Earth from the ground.  What happens is that when it is dark on the ground, but still light at orbital altitudes (around 250 miles high and above), sunlight can reflect off the satellite and it can look like a star in the sky.  This happens just after sunset or just before sunrise.  If you are very patient and look up at the sky during these times (preferably from an outdoor hot tub), you can sometimes see objects that look like stars that are moving from south to north or north to south. To give you an idea, it should take them about 10 minutes to go from horizon to horizon.

The Humanity Star is so bright that it should be be visible during the day.  The web page talks about how this will be a beacon to draw humanity back together and to make them look to the stars.  I personally don’t think that a tiny star-like object in the sky will bring humanity back together unless the star-like object is getting bigger and bigger every day and has the potential to wipe out humanity.  Other people that I have talked to have a similar feeling, and so it seems like The Humanity Star really has no real value. Except it does. There are a few good reasons, some intended, and others maybe not.

Humanity-Star-2
The Humanity Star. It is not in orbit in this picture. It is sitting on the ground. (From the website).

The true purpose of The Humanity Star was really to test the Electron rocket by Rocket Lab. This was the first flight of the Electron.  While Space-X just launched the Falcon Heavy, Rocket Lab launched a small rocket that can take only 150-225 kilograms to orbit for an estimated price of $5M.  This is a huge deal because constellation missions would like to spread out satellites.  It is incredibly difficult to truly distribute a constellation of satellites from a single launch vehicle (rocket).  If you could buy 8 tiny rockets that could take one or two satellites to orbit for the price of one medium sized rocket that could take 8 satellites, it would allow you to distribute the satellites immediately.

When you test a rocket for the first time, the probability of failure is quite high (like, explosively high).  Some companies give a special deal to satellite companies to launch their satellite on a very risky rocket launch. If it blows up, then everyone loses, but they are not out a huge amount of money.  If it doesn’t blow up, everyone wins – the rocket is proven to work, and the satellite gets to orbit for cheap. Other companies just launch dummy payloads in order to prove that the rocket works.  If it works, then they have a proven rocket.  If it doesn’t, no one is harmed.  This path doesn’t make the company any money (if the rocket works), but also doesn’t make people really angry (if it doesn’t work).

The Humanity Star was a dummy payload for the first test launch of the Electron rocket.  This is similar to Space-X launching a Tesla on the Falcon Heavy (another dummy load with an actual dummy in the driver’s seat). Instead of just saying that it was a test load, Rocket Lab made a big deal about The Humanity Star instead of talking about their super cool and super small rocket.

The second interesting thing about The Humanity Star is that it can actually be used to do science, even though it has no power or sensors or anything. The Air Force has many dummy spheres like this in orbit. The reason for this is that all objects in low Earth orbit feel atmospheric drag.  Since the projected area of a nearly spherical object is known exactly and basically never changes (since it looks exactly the same from every angle) the only change in the drag force that the object feels is due to changes in the atmospheric density. Normal satellites are strange shapes and have lots of protrusions, like antennas and such.  If the orientation of the satellite changes, the drag changes. It is often extremely difficult to model this behavior accurately.  So, simple spheres are used and are tracked with radars from the ground.

The Humanity Star will allow us to more accurately track the thermospheric density since it is really big (about 1 meter across) and pretty light (about 8 kg).  Its area to mass ratio means that the drag that it feels will be pretty big, so it will reenter the atmosphere pretty quickly (less than a year). Because it feels such a large drag, the drag force will be easy to determine and any changes will be caused by only by changes in the thermospheric density.  This is the type of research that I do!

Another really minor thing about The Humanity Star is that because it can be visible from just before sunrise to just after sunset, including the whole day, it could be used for educational purposes.  You see, a satellite’s orbit can be determined just by tracking how it moves across the sky.  If you point a telescope at the satellite in the sky and mark down the direction that the telescope is pointed, and do this over and over again as the satellite moves across the sky, the math is relatively easy to do to determine the orbit (well, students do this in Junior-level Aerospace Engineering classes). This is a great real life example that students could use to put their education to use! In the daylight!

Hopefully this has convinced you that The Humanity Star is not a complete waste of time and money!

 

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