Mission Concept and Vision
The SkyHopper mission is currently the first cubesat concept for an infrared space telescope, with a tentative launch date at the end of 2021. Thanks to its near-infrared sensitivity, ultra-stable image quality in four simultaneously exposed filter bands, and rapid spacecraft slewing, SkyHopper will be the world-leading facility to identify Gamma Ray Burst (GRB) afterglows originating from the edge of the observable Universe, and to discover/characterize potentially habitable Earth-size exoplanets transiting in front of nearby cool stars.
Key Science Goals
- Search for other Earths
The current focus of exoplanetary science is the discovery and characterisation of potentially habitable Earth-size planets around cool stars. Space observations are crucially needed to achieve sufficient photometric stability. With its near-IR camera, SkyHopper will be highly complementary to NASA’s upcoming Transiting Exoplanet Survey Satellite (TESS), which will identify the nearest, short-period planets from all-sky data at optical wavelengths. SkyHopper will be highly efficient for follow-up of TESS targets to measure masses through transit timing variations and to identify longer-period planets at larger distances, in the habitable zone where water can exist in a liquid state. Based on simulations, SkyHopper is expected to double the TESS yield for habitable-zone Earth-sized exoplanets. In addition, it will also be highly competitive for carrying out a new transiting survey around brown dwarfs (similar to the recently discovered multi-planetary system TRAPPIST-1). Overall, SkyHopper will become the premier facility for exoplanet IR transits and a very effective and productive successor to NASA’s Spitzer Space Telescope for exoplanet science.
- Identify Gamma Ray Bursts in the first billion years after the Big Bang
SkyHopper will follow-up GRB triggers with near-IR photometry, identifying candidate bursts at redshift z > 5, with an expected discovery rate of 5 ± 2 yr-1. The efficiency gain of prompt near-IR imaging from space is so significant that within two years of operations following up events discovered by the SWIFT satellite, SkyHopper is expected to double the sample size of known GRBs at redshift z > 5 as collected by the whole community over more than 20 years. This would enable new exciting opportunities to leverage SkyHopper’s discoveries to investigate the formation of massive stars and of their host galaxies during the epoch of reionization, a time when the gas in the Universe underwent a complex phase transition and the first heavy chemical elements begin being produced.
- Measure the Cosmic Infrared Background
Just as the Cosmic Microwave Background radiation encodes the astrophysics in the aftermath of the Big Bang, the Cosmic Infrared Background (CIB) contains the entire integrated history of nearly everything that has happened since the formation of stars. The CIB directly probes all aspects of galaxy formation and evolution: star-formation, supernova, stellar evolution, dust production, and supermassive black hole emission. Measuring it
directly requires a space telescope to avoid the highly variable infrared glow of Earth’s atmosphere, and accurate subtraction of the Zodiacal light. The measurement has been attempted with the Hubble and Spitzer Space Telescopes, and with sounding rockets, but uncertainties remain large. SkyHopper will dedicate months of observations to the CIB and employ a highly optimized Zodiacal light subtraction, by simultaneously measuring it with a narrow-band Ca II triplet filter while acquiring broadband imaging. With this strategy, SkyHopper’s data will enable for the first time use of the CIB to constrain the history of star formation back to the Epoch of Reionization.
- Explore the time-variable Universe
The search for IR counterparts of transients identified across a range of electromagnetic wavelengths and other messengers like gravitational waves, neutrinos, and cosmic rays is an increasingly important field in astrophysics. SkyHopper’s IR coverage and rapid spacecraft slewing are ideally suited to investigate short-lived transients occurring in highly obscured environments such as star-forming regions.
- Unveil planetary system formationSolar System dust clouds and asteroids are fossil remnants from the epoch of planet formation. Yet current studies on the origin of these objects leave multiple origin scenarios open, mainly because of the difficulties in carrying out detailed observations of Near-Earth Objects with multi-day sequences at high cadence in the infrared, which are needed to characterize spin, binarity, and spectral classification. SkyHopper’s space observations will bypass these ground-based limitations, determine the collisional history and surface mineralogy of Near-Earth Objects, providing clues on how planetary systems form.
The spacecraft concept is based on a 12U format (∼ 36 × 22 × 24 cm3), which will house a 20 × 10 cm2 rectangular telescope mirror, feeding light to a 2048×2048 IR image sensor (H2RG) actively cooled to 145 K. SkyHopper’s camera design is based on a novel concept using a 3-mirror anastigmat feeding a dichroic Kester-type prism, which splits the light spectrally into 4 adjacent, ∼ 0.2 μm wide and simultaneously exposed filter bands, each covering the same field of view on the sky. The spacecraft attitude will be controlled by three miniature star trackers and four reaction wheels, capable of slewing to new targets at 3 deg s−1 and of maintaining a pointing accuracy better than 4” (68% confidence), comparable to the telescope’s angular resolution. A sat-phone duplex modem will provide 24/7 uplink and downlink for low-bandwidth but time- critical communications, complementing a high-throughput (3 Mbit s−1) radio antenna for large data transfer. These features will give SkyHopper an ultra-rapid response to transient events, 1000 times faster than the Hubble Space Telescope. The combination of timeliness on target and low background/stable image quality from space at infrared wavelengths make SkyHopper a unique facility that augments the capabilities of ground and space-based telescopes that are 100 to 1000× more expensive (Hubble, James Webb, 30-meter class observatories).
Key Mission Specifications
- 12U cubesat in Sun-synchronous polar orbit (∼ 600 km) with ≥ 48 months orbital lifetime.
- Highly stabilized spacecraft (<4′′ RMS pointing stability).
- 24/7 Sat-phone uplink & rapid slew (3 deg/s) for prompt repointing to new coordinates (< 120 s from trigger if target is visible).
- Telescope: 3-mirror anastigmat (200 cm2 aperture); > 0.25 × 0.25 deg2 field of view; diffraction limited; efficient baffling (SWIFT-like Sun, Earth, Moon avoidance angles).
- Actively cooled near-IR detector; dichroic prism for 4-band simultaneous imaging (0.8-1.7 μm).
- Point source sensitivity: mAB = 19.5 [t = 600 s; 5σ; H band].
2016 Mission formulation; preliminary concept design;
2017 Seed funding secured: preliminary design; dichroic imager model;
2018 Preliminary design (cont.); dichroic imager model (cont.); cryocooler testing;
2019 Final design; construction;
2020 Construction (cont.);
2021 System assembly; integration; testing; launch;
2022+ Commissioning; operations [nominal 2yr; extended 4yr]; start constellation program.
The Consortium: Leadership Highlights
A/Prof. Michele Trenti (Melbourne): Principal Investigator
Dr. Lee Spitler (Macquarie): Cosmic Infrared Background science lead
A/Prof. Michael Ireland (ANU): Exoplanet science co-lead
Dr. Jon Lawrence (AAO/Macquarie): Telescope working group co-lead
Prof. Michael Skrutskie (UVa): Telescope & detector design; Exoplanet science
Dr. Jochen Greiner (MPE): Telescope working group co-lead; GRB science lead
Dr. Nikku Madhusudhan (Cambridge): Exoplanet science co-lead
A/Prof. Katherine J. Mack (NCSU): Media and Outreach lead; Transient science
Mr. Robert Mearns (Melbourne): Systems Engineer
- Measure the Cosmic Infrared Background