Apollo Telescope Mount

Lore & Background

The ATM originated from the late 1960s Apollo Applications Program, which explored extended lunar missions, a permanent lunar base, long-duration space missions, and large observatories. Initially conceived as a deployable unit attached to the Apollo Service Module, the design evolved to use a modified Apollo Lunar Module, with the descent stage replaced by a large solar telescope and solar panels. After launch, it was to be met in orbit by a three-crew Apollo CSM. As other concepts were dropped, only the space station and ATM remained, and plans shifted to launch the ATM to connect with Skylab in orbit, later changed to launch the ATM attached to the station on a Saturn V.

During Skylab's launch, a problem destroyed one workshop solar panel and prevented another from deploying. The ATM's windmill-like solar arrays, protected within the launch shroud, remained undamaged and provided enough power for crewed operations until the remaining workshop array was deployed on the first crewed mission. The ATM was actively cooled, and pointing was controlled by the Skylab computer, commanded by astronauts or from Earth. Film canisters had to be changed during spacewalks; the heaviest weighed 40 kg and held up to 16,000 frames. Some instruments provided live video feed, and some of the first Polaroid photos in space were taken of a Skylab CRT screen displaying the Sun from an ATM instrument.

Reader's Guide

The Apollo Telescope Mount was significant as the first crewed solar observatory in space, providing a unique platform for sustained, hands-on observation of the Sun across multiple wavelengths. Its data, returned as photographic film, yielded over 150,000 exposures that remained accessible at the Naval Research Laboratory as of 2006. The ATM's legacy includes its critical role in saving the Skylab program after the launch damage, as its solar arrays supplied essential power. A backup ATM spare was restored and put on display in 2015 at the Steven F. Udvar-Hazy Center. The ATM demonstrated the value of human-tended space observatories and contributed to solar physics through its eight major instruments, including X-ray telescopes, ultraviolet spectrographs, and a visible-light coronagraph.

Did You Know?

• The ATM provided about 30% of Skylab's electrical power via its four X-shaped solar panels.
• Film canisters for the ATM were among the heaviest items returned to Earth, with the heaviest weighing 40 kg (88.1 lb).
• A backup ATM spare was restored and put on display at the U.S. Space & Rocket Center in Huntsville, Alabama.

From Lunar Module to Space Station: The ATM's Shifting Identity

The ATM's story began in the late 1960s within NASA's Apollo Applications Program, which explored how to leverage the infrastructure built for the Moon landings into new 1970s endeavors. Among the many concepts studied—extended lunar stays, a permanent base, long-duration missions, and large observatories—the solar telescope concept eventually survived as one of only two projects still on the books. Early designs envisioned mounting instruments on a deployable unit attached to the Apollo Service Module, then shifted to housing them in a modified Lunar Module whose descent stage would be swapped for a solar telescope and power arrays. A three-crew Apollo Command/Service Module would rendezvous in orbit to operate and retrieve data. As other Apollo Applications concepts were cancelled, the plan evolved: the ATM would connect to Skylab in orbit, and ultimately, freed by the cancellation of later Moon landings, a Saturn V could launch the ATM and the expanded dry workshop together. The name Apollo persisted from these early spacecraft-tethered roots, even though the final launch vehicle was the Saturn V and the station was called Skylab.

Eight Instruments, One Active-Cooled Observatory

The ATM housed eight principal solar-observation instruments plus several smaller experiments, collectively spanning wavelengths from 2 to 7,000 angstroms—covering soft X-rays, ultraviolet, and visible light. The suite included two X-ray telescopes (designated S-054 and S-056), an X-ray and extreme-ultraviolet camera (S-020), an extreme-ultraviolet spectroheliograph (S-082A), an ultraviolet spectroheliometer (S-082B), an ultraviolet spectrograph (S-055), a visible-light coronagraph (S-052), and two Hydrogen-alpha telescopes. An additional experiment, S-149, was mounted on one of the solar panels. The entire assembly was actively cooled to keep instruments within a narrow thermal window, and pointing was handled by the Skylab onboard computer, which astronauts could command from inside the station or via a communication link from Earth. Design and construction were managed at NASA's Marshall Space Flight Center, and the mount underwent thermal-vacuum testing before flight. Four external solar panels deployed in an X configuration, supplying roughly thirty percent of the station's total electrical power.

Fifty Thousand Frames in Spacewalks and Space

Six of the ATM's experiments recorded their observations on photographic film, and across the Skylab missions the crew logged more than 150,000 successful exposures. Nearly thirty film canisters were loaded, used, and brought back to Earth. Each canister could hold up to 16,000 frames, and the heaviest weighed around 40 kilograms—making them among the most massive items the crew had to haul back into the Apollo capsule at the end of every mission. Because the instruments were external, astronauts had to perform spacewalks to physically swap out the spent canisters. A few instruments also provided a live video feed viewable from inside the station, and in one memorable instance, astronauts captured some of the first Polaroid instant photographs taken in space by photographing a CRT monitor displaying an ATM solar image. The original film exposures, as of 2006, remained on file at the Naval Research Laboratory in Washington, D.C., accessible to researchers and the public.

The Panels That Saved Skylab, and a Legacy in Glass and Kapton

The ATM's solar arrays played an accidental but critical role in saving the Skylab program. During launch, a problem destroyed one of the workshop's own solar panels and jammed the other, leaving the station nearly powerless. The ATM's four windmill-shaped panels, protected inside the launch shroud, emerged undamaged and delivered enough electricity for crewed operations until astronauts deployed the surviving workshop array on the first mission. This contingency, born of the decision to launch the ATM and station together on a single Saturn V, turned a potential catastrophe into a manageable repair. Decades later, a backup ATM unit—its instruments still mounted—was restored and installed for public display in 2015 at the Steven F. Udvar-Hazy Center in Chantilly, Virginia. The restoration required repairing Kapton layers that had degraded over four decades of storage. Together, the surviving hardware and the archived film record ensure that the ATM's solar science continues to be studied long after the Skylab crews returned home.