NASA wants ideas to boost Hubble Space Telescope into a higher orbit with private spaceships

On Dec. 22, the space agency issued a Request for Information regarding a non-exclusive SpaceX study earlier this year that suggested how the Hubble Space Telescope could be "reboosted" into a higher orbit.

Since the start of Hubble's operations in 1990, the orbit of the space telescope 335 miles (540 kilometers) above Earth has been decaying. Reboosting it to an orbit that is both higher and more stable could add years to Hubble’s operating lifetime delaying the point at which NASA must deorbit or dispose of the telescope.

During its five space shuttle missions to the service Hubble, NASA used the shuttle to reboost the telescope. The last shuttle servicing mission to Hubble was in 2009. NASA retired its shuttle fleet in 2011.

The idea to raise Hubble to a higher orbit using a Dragon spacecraft at no cost to the government was first developed between SpaceX and Polaris Program, a private program of space missions using SpaceX's Dragon and Starship vehicles funded by billionaire Jared Isaacman. The unfunded agreement between SpaceX and NASA to study the feasibility of reboosting Hubble was then signed in September 2022.

The SpaceX study was designed to help NASA, which currently has no plans to operate or fund a new Hubble servicing mission, determine the commercial possibility of such a mission. The SpaceX study also aimed to lay out the technical challenges of such a servicing endeavor.

First, understand that aerodynamic drag changes at the square of the change in velocity. That means drag increases exponentially with speed, and Hubble is going about 17,000 mph. At those kinds of speeds even tiny amounts of gas eventually will cause a decay of orbital velocity.

Second, there are traces of gas well outside what is regarded as the limits of earth's atmosphere. Geosynchronous orbit is a little above 22,000 miles (Hubble is less that 400 miles) and there's enough gas floating around -- even at that altitude -- that the satellites in Geosync need the occasional boost.

Space junk that's too big to de-orbit gets thrown out to "graveyard" orbit, 22,400 miles, about 180 miles beyond geosync. Even space junk that's in "graveyard" orbit eventually will fall back to earth, but in some cases that isn't predicted to happen for millions of years. Nonetheless, even that high, eventually aerodynamic and gravity wave drag will bring them back to earth.

I guess NASA is counting on Future Man to have a landing net big enough to catch them when they eventually come home.

The deal with Hubble is that NASA was ready to pull the plug and let it de-orbit, particularly with Webb now on station. But Hubble isn't entirely obsolete (and Webb can't be looking everywhere at once) so this in part is as much an experiment for its own sake as it is an effort to keep Hubble in service.

No doubt they'll use a Hohmann transfer to boost Hubble. That means they won't push vertically, they'll push horizontally, sideways. As the satellite gets faster it naturally goes higher (centripetal force).

Orbits by nature tend to be elliptical (Kepler's first law of orbital motion) and special measures have to be taken to make them more nearly circular (a circle is a special case of an ellipse). Hubble's current orbit is very nearly (but not entirely) circular and if they want the new orbit to be circular, too, it will take two boosts because the new orbit initially will be elliptical. It will take a second boost, with firing beginning when the satellite is at the point in the new orbit that's furthest away from earth (at apogee),

The initial boost begins at apogee for the old orbit, which becomes perigee for the new orbit (labeled point P) and establishes an elliptical orbit through a new apogee (point A). If they feel the need, a second firing at Point A can give them back Hubble's original nearly circular orbit.

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