On the Hunt for Asteroids: Positioning an Occultation Telescope

The digital video stream from the camera on TAOT is fed into software that can monitor the target star and determine when it disappears and reappears. The drop in light from the star, though subtle, is easily detected by the reduction software. The time of disappearance is shown by the red dashed line, and the reappearance by the green dashed line. (Image: Vince Sempronio, Winer Observatory)

Several books and movies have been made depicting an asteroid or comet striking the Earth. There is a small chance of such an event, but if it happens, the results could be devastating, perhaps even causing a mass extinction event such as the one many believe killed off the dinosaurs 65 million years ago. It is potentially the largest preventable natural disaster. And that’s why the Winer Observatory in Arizona is working on planetary defense by tracking NEOs (Near Earth Objects). HEIDENHAIN donated encoders to assist in the positioning for their newest portable telescope project that will enable Winer to do just that.

HEIDENHAIN donated two encoders to enable the new Transportable Asteroid Occultation Telescope (TAOT) at the Winer Observatory to find and record occultation events. (Image: Vince Sempronio, Winer Observatory)

“Early detection of a NEO headed for Earth would give us sufficient time to deflect the threat,” said Vince Sempronio, Lead Observer at Winer Observatory, who specializes in observing planet (asteroid) occultations and is also involved with educating area groups on astronomical science. An occultation occurs when an astronomical body, such as a NEO, moves in its orbit around the Sun and comes between an observer on Earth and a distant star. When the NEO is directly between an observer and the star, the star (usually brighter than the NEO) winks out or is occulted by the NEO. Those events provide information about the orbit, size, and shape of the asteroid that can be used to reduce the chance of it hitting Earth.

The development of Winer’s new telescope took over a year in the making and was designed to be uniquely transportable. With a 16-inch diameter mirror set within a relatively small structure on wheels, it is an unusual tool for astronomers as it is an extremely high accuracy telescope that can be moved by car.

The structure includes two HEIDENHAIN incremental encoders that provide accuracy for the telescope’s movement and placement on the star(s), meeting Winer’s accuracy requirements for each encoder count to represent 1 to 2 arc minutes on the sky.

The size and shape of an asteroid can be determined using several observers on multiple tracks (in this case, five separate tracks) via TAOT. This is possible when a target asteroid moves between the observer on Earth and the distant star. (Image: Vince Sempronio, Winer Observatory)

The telescope named the Transportable Asteroid Occultation Telescope (TAOT) includes a video camera located at its prime focus set to record occultation events. Instead of an eyepiece, the TAOT uses a very low light level surveillance TV camera taking 25 frames per second (PAL — the European TV standard) or 30 frames per second (NTSC — the American standard). The video data is digitized and recorded on a tiny computer. After the event, the user can process the data using analysis software sensitive to tiny drops in the combined light of the star and NEO that shows the event far better than the human eye can simply by watching the occultation.

TAOT’s camera has a field of view of a few arc seconds on a side. After aligning the telescope on a couple of stars, users slew the telescope to their target field. “We needed the encoder feedback to ensure the telescope is pointed at the correct star to be occulted,” said Sempronio, “and we are thrilled to now have harnessed this level of accuracy with the help of HEIDENHAIN and their two ROD 426 encoders.”

A HEIDENHAIN ROD 426 angle encoder is incorporated into the building of TOAT to ensure accurate pointing on the stars. (Image: Vince Sempronio, Winer Observatory)

In late 2021, HEIDENHAIN donated two ROD 426 incremental shaft angle encoders to enable the Winer Observatory to further its cause. These encoders offer “5000 ticks” (in TTL format) per revolution of the shaft. There are two such outputs, out of phase with each other by 90 degrees. Appropriate electronic circuitry in typical commercial small telescope control systems converts these two outputs into a count that is four times the physical tick count in the encoder. So, 4 x 5000 = 20,000 counts per revolution.

There are 21,600 arc minutes in each one complete rotation of the telescope in either axis [(60 arc minutes) x (360 degrees) = 21,600]. This means TAOT can easily meet the requirement for each encoder count to represent 1 to 2 arc minutes on the sky. Incorporating these encoders on the TAOT structure will permit easy alignment of the telescope to known bright stars with accuracy sufficient to point the telescope to a target star that is very much fainter (typically, cannot be seen with the unaided eye).

Once aligned on those known stars, the user can slew the telescope to the target star and watch it on a small screen attached to the camera showing what the powerful camera sees and begin recording for subsequent analysis.

This new highly portable telescope can be moved to shadow paths of asteroid occultations. It is promising to contribute to a substantial increase in the understanding of an asteroid’s orbit (which helps with predicting whether it will collide with the earth), shape and size (which helps in determining the damage that would result from impact).

Early detection of an NEO headed for Earth would give governments sufficient time to deflect the threat. In late 2021, NASA launched the Double Asteroid Redirection Test (DART) to an asteroid to test the kinetic Impactor technique for planetary defense. That is, to send a spacecraft to crash into an asteroid to change its orbit just enough to make a difference. DART hit the asteroid in September 2022 and altered its path. The earlier we detect a threat, the larger the distance we can move the asteroid with this technique.

“Occultation events occur on their own time and the observer does not have the luxury of hunting around for just the right star. This encoder donation is enabling us to increase the number of occultations observed,” said Mark Trueblood, Director of the Winer Observatory. “Without this generous gift, we would need more time to find the star to be occulted. This could spell the difference between success and failure in making these critical observations.”

This article was contributed by HEIDENHAIN Corporation (Schaumburg, IL). For more information, visit here .