astronomy

Sentinel Space Telescope

Sentinel Space Telescope is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sentinel Space Telescope rather than just read about it. In short: The Sentinel Space Telescope was a space observatory to be developed by Ball Aerospace & Technologies for the B612 Foundation. The B612 Foundation is dedicated to protecting the Earth from dangerous asteroid strikes and Sentinel was to be the Foundation's first spacecraft tangibly to address that mission.

Key takeaways

Sentinel Space Telescope belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sentinel Space Telescope to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sentinel Space Telescope from memory before moving on to harder problems.

Reference excerpt

The Sentinel Space Telescope was a space observatory to be developed by Ball Aerospace & Technologies for the B612 Foundation. The B612 Foundation is dedicated to protecting the Earth from dangerous asteroid strikes and Sentinel was to be the Foundation's first spacecraft tangibly to address that mission. The space telescope was intended to locate and catalog 90% of the asteroids greater than 140 metres (460 ft) in diameter that exist in near-Earth orbits. The telescope would have orbited the Sun in a Venus-like orbit (i.e. between Earth and the Sun). This orbit would allow it clearly to view the night half of the sky every 20 days, and pick out objects that are often difficult, if not impossible, to see in advance from Earth." Sentinel would have had an operational mission life of six and a half to ten years. After NASA terminated their funding agreement with the B612 Foundation in October 2015 and the private fundraising goals could not be met, the Foundation eventually opted for an alternative approach using a constellation of much smaller spacecraft under study as of June 2017. NASA/JPL's NEOCam has been proposed instead.

History The B612 project grew out of a one-day workshop on asteroid deflection organized by Piet Hut and Ed Lu at NASA Johnson Space Center, Houston, Texas on October 20, 2001. Participants Rusty Schweickart, Clark Chapman, Piet Hut, and Ed Lu established the B612 Foundation on October 7, 2002. The Foundation originally planned to launch Sentinel by December 2016 and to begin data retrieval no later than 6 months after successful positioning. In April 2013, the plan had moved out to launching on a SpaceX Falcon 9 in 2018, following preliminary design review in 2014, and critical design review in 2015. As of April 2013, B612 was attempting to raise approximately $450 million in total to fund the total development and launch cost of Sentinel, at a rate of some $30 to $40 million per year. That funding profile excludes the advertised 2018 launch date.

Cancellation After NASA terminated their $30 million funding agreement with the B612 Foundation in October 2015 and the private fundraising did not achieve its goals, the Foundation eventually opted for an alternative approach using a constellation of much smaller spacecraft which is under study as of June 2017. NASA/JPL's NEOCam has been proposed instead.

Mission

Unlike similar projects to search for near-Earth asteroids or near-Earth objects (NEOs) such as NASA's Near-Earth Object Program, Sentinel would have orbited between Earth and the Sun. Since the Sun would therefore always have been behind the lens of the telescope, it would have never inhibited the telescope's ability to detect NEOs and Sentinel would have been able to perform continuous observation and analysis. Sentinel was anticipated to be capable of detecting 90% of the asteroids greater than 140 meters in diameter that exist in Earth's orbit, which pose existential risk to humanity. The B612 Foundation estimates that approximately half a million asteroids in Earth's neighbourhood equal or exceed the one that struck Tunguska in 1908. It was planned to be launched atop the Falcon 9 rocket designed and manufactured by the private aerospace company SpaceX in 2019, and to be maneuvered into position with the help of the gravity of Venus. Data gathered by the Sentinel Project would have been provided through an existing network of scientific data-sharing that includes NASA and academic institutions such as the Minor Planet Center in Cambridge, Massachusetts. Given the satellite's telescopic accuracy, Sentinel's data was speculated to prove valuable for future missions in such fields as asteroid mining.

Specifications

The telescope was intended to measure 7.7 metres (25 ft) by 3.2 metres (10 ft) with a mass of 1,500 kilograms (3,300 lb) and would have orbited the Sun at a distance of 0.6 to 0.8 astronomical units (90,000,000 to 120,000,000 km; 56,000,000 to 74,000,000 mi) approximately in the same orbital distance as Venus. It would have employed infrared astronomy methods to identify asteroids against the cold of outer space. The B612 Foundation worked in partnership with Ball Aerospace to construct Sentinel's 0.51 m (20 inches) aluminum mirror, which would have captured the large field of view. "Sentinel will scan in the 7- to 15-micron wavelength using a 0.5-meter infrared telescope across a 5.5 by 2-deg. field of view. The [infrared] IR array would have consisted of 16 detectors, and coverage would have scanned a 200-degree, full-angle field of regard."

Features Key features included:

Most capable NEO detection system in operation; 200 degree anti-sun field of regard, with a 2×5.5 degree field of view at any point in time: scans 165 square degrees per hour looking for moving objects; Precise pointing accuracy to sub-pixel resolution for imaging revisit, using the detector fine steering capability; Designed for highly autonomous, reliable operation requiring only weekly ground contact; Designed for 6.5 to 10 years of surveying operations. Actively cooled to 40K using a Ball Aerospace two-stage, closed-cycle Stirling-cycle cryocooler; Ability to follow up on objects of interest.

Issues

REP. STEWART: ... are we technologically capable of launching something that could intercept [an asteroid]? ... DR. A'HEARN: No. If we had spacecraft plans on the books already, that would take a year ... I mean a typical small mission ... takes four years from approval to start to launch ...

Illustrations

Worked examples

Example 1 — a first encounter with Sentinel Space Telescope

Start with the simplest possible case. Write down what Sentinel Space Telescope claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sentinel Space Telescope before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sentinel Space Telescope ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sentinel Space Telescope

In research: Sentinel Space Telescope appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sentinel Space Telescope in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sentinel Space Telescope is common in secondary-school and first-year university syllabi. It links to neighbouring topics Asteroid surveys, Infrared telescopes, Minor-planet discovering observatories, so understanding it makes those chapters shorter.
In everyday life: Look for Sentinel Space Telescope outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sentinel Space Telescope in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sentinel Space Telescope means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sentinel Space Telescope out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sentinel Space Telescope in simple terms?

Why does Sentinel Space Telescope matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sentinel Space Telescope?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sentinel Space Telescope.