Description of the payload

Sunrise is a light-weight solar telescope created to make spectro-polarimetric observations of the atmosphere of our Sun.

The instrumentation consists of a main telescope with an aperture of 1 m, feeding three focalplane instruments: the spectrograph-polarimeter, the filtergraph, and the magnetograph. The focal-plane package is mounted piggy-back on the telescope structure.

The central scientific aim of the instrument is to try to understand the structure and dynamics of the magnetic field in the solar atmosphere and the chromosphere as well to understand the physics of irradiance changes.

The main telescope has an aperture of 1 m and consists of a parabolic primary mirror with a focal length of 2.5 m and an elliptic secondary mirror thus providing a effective focal length near 25 m. It has a Gregorian configuration, with the primary image formed between the two mirrors.

The kind of observations to be done requires a very high spatial resolution down to 0.05 arcsec. and implies a substantial effort to accurately point and guide the telescope. In order to reach this goal, the pointing and guiding system works on two levels, first for solar pointing of gondola/telescope in azimuth by a torque motor drive as part of the momentum transfer unit (MTU) at the gondola support point, and second by precision guiding, and compensation of image motion.

Because of the large temperature differences between ground and flight conditions it is important to have reliable and accurate in-flight alignment capabilities. So a wavefront control system was developed, that is capable of detecting low-order modes of wavefront deformations in the telescope. A wavefront sensor measures the actual state of the optical alignment and generates an appropriate error signal. A control system converts this error signal into actuation signals which are used to drive the position of the secondary mirror, and the tip-tilt mirror.

Let's see in detail the three instruments coupled to the telescope. First, the spectrograph-polarimeter (SP) combines high-resolution vector-polarimetry with a multi-line Echelle spectrograph in a modified Littrow configuration, simultaneously providing photospheric magnetic field measurements and diagnostic spectroscopy of photospheric and chromospheric lines.

Second, the filtergraph (FG) is realized as a multiwavelength slit-jaw camera of the spectrograph polarimeter. This allows both instruments to receive the full amount of light in all wavelengths. In addition, the image of the spectrograph entrance slit in the filtergrams allows a precise identification of the region simultaneously observed with the SP. Three wavelengths each are chosen to sample the photosphere and the chromosphere.

Finally, The Imaging Magnetograph Experiment for Sunrise (IMaX) is an imaging vector magnetograph based upon narrow-band filters. The instrument provides fast-cadence two-dimensional maps of the complete magnetic vector and the line-of-sight velocity with high spatial resolution. IMaX images are taken in two narrow wavelength bands whose selection is made by a tunable system of Fabry-Perot etalons in a telecentric path. In this way, one ensures the homogeneity of the selected wavelength over the field of view.

The Sunrise telescope is mounted on the elevation axis to a gondola consisting of standard aluminium components. It is designed to withstand the vertical acceleration that is applied to the attachment rings when the parachute is opened near the termination of the flight. This structure and aeroflex shock absorbers protect the payload from the vertical and horizontal components of the landing shock load in case of landing in cross winds. The gondola can be moved in azimuthal direction to point the telescope and the solar panels towards the Sun. This is realized by means of a momentum transfer unit (MTU) mounted at the top of it, designed to minimize jitter in pointing stability.

During ascent, descent, and landing, the telescope is stowed horizontally, so that it is protected by the so called 'cradle'. The gondola is suspended from the main telescope frame and rotates with its structure while the telescope is being driven directly via the MTU.

Video of the launch operations

Details of the balloon flight and scientific outcome

 

Launch site: European Space Range, Kiruna, Sweden  
Balloon launched by: Columbia Scientific Balloon Facility (CSBF)
Balloon manufacturer/size/composition: Zero Pressure Balloon  
Flight identification number: 596N

SUNRISE was launched on Monday, June 8th, at 6.27 utc by dynamnic method using the Hercules launch vehicle. The gondola was smoothly released and the balloon started the ascent at a rate a little more slowly than anticipated. The absence of strong winds on the surface provoked the balloon to ascend directly overhead of ESRANGE until reached float altitude of 121.400 feet when it started to flew in a westward path crossing over Sweden, Norway and started to cross the Atlantic Ocean.

The route that the balloon developed was more northernward than expected so the flight was a little shorter than planned not to risk a sea landing of the payload. In the last hours of June 13 the scientific team transmitted the command to put the instrument in landing mode. Flight was terminated on June 13 at 22:52 UTC after a flight of 5 days, 17 hours, and 18 minutes.

The termination was conducted using over the horizon procedures through the Palestine Operations Control Center, while the standard semi-automatic parachute release was performed by the flight crew in the chase aircraft.

The payload landed in Somerset Island, 68 nautic miles S-SE of the nearest airfield located in Resolute Bay, Nunavut, Canada. During the first minutes the chase plane was not able to see the payload due to adverse cloud cover including very low ceilings in the landing site. However, the crew confirmed the parachute separation and the Palestine center continued to receive Iridium transmissions for an extended period after impact, indicating that the payload was in good condition.

Sunrise was completely recovered a few days after landing. All instrument parts were flown out via helicopter first to Resolute Bay, then with airplanes to Yellowknife, where the equipment was packed into sea containers for shipment to their home institutions. Damage to Sunrise was found to be moderate, e.g.the primary mirror survived the landing perfectly intact. The scientific data stored on the data storage harddrives safely arrived at MPS on June 25, 2009, being handcarried directly from Yellowknife on commercial airplanes.

This was the first scientific flight of SUNRISE after a first engineering flight test performed in Fort Sumner, New Mexico in 2007. The mission was planned to coincide with the quietest period of solar magnetism activity in nearly a century.

During this Transatlantic flight, all systems on board performed flawlessly. In the initial phase of the flight the scientific team encountered some troubles with the communications. Until SUNRISE disappears beyond the horizon from the launch base they can communicate via a fast line-of-sight data link, a very important feature, since in this initial phase and before tha balloon drifted over the Ocean was neccesary to calibrate the onboard instruments. To allow a more longer high data rate link with the balloon was intended to use a second ground station in the Lofoten archipelago off the coast of Norway assuring a minimum of fast data link for ten to twelve hours. Unfortunately, the transfer to the Lofoten station didn't worked and therefore, they had to switch to the low rate system via satellite so calibration took longer than expected.

On the first day of flight were started up the scientific instruments. The pictures received via satellite were of not much resolution but they were enough detailed to confirm the excellent quality of the observations performed.

Through the flight the telescope worked perfectly and all the instruments worked at predicted temperatures. Even after a complete day-night-cycle with the associated temperature changes the high image quality not changed and the telescope remained perfectly focused.

Close observations of sunspots that appeared during the flight were performed in a coordinated manner with several other solar telescopes in the entire world, to allow a comparation of the results later.

The near 130 hours of observations obtained during the flight equals almost two terabytes of data. Those images of the Sun helped to understand the relationship between magnetic fields and the brightness of the magnetic structures in the ultraviolet; a critical study that is helping the scientists to understand the impact of solar ultraviolet radiation on the chemistry of the polar stratosphere.

A second mission was performed in June 2013, this time during a period of maximum activity.

External references and bibliographical sources

Images of the mission

The entire SUNRISE team infront of the instrument before launch from Kiruna, Sweden (Image: IMAX team) View of the launch pad during inflation of the SUNRISE balloon (Image: SSC) The balloon was released and is moving downwind to take the payload (Image: SSC) Another view of the SUNRISE balloon launch from a nearby hill (Image: SSC) Rescue team possing in front of SUNRISE in the impact point at Somerset Island (Image: SSC)