SUBMILLIMETRON project

Development of a Submillimeter Wave Criogenic Telescope
for the Russian Segment of International Space Station. 

1. Introduction and objectives

The objectives of the Submillmetron Project are twofold. The primary goal is to perform an astronomical study in submillimeter and infrared wavelengths of the "cold" component of the matter in the Universe (dust in the Solar System, in the Galaxy, and in extragalactic sources, etc.), to conduct a submillimeter wave survey, to perform studies of the spectra of astronomical sources and their variability, to conduct cosmological studies (study of the anisotropy of the cosmic microwave background radiation and search for Lyman-alpha line at the epoch of recombination and secondary heating). The secondary goal is to provide a test bed to perform the technological experiments needed to develop follow-on projects.

The Submillimetron Project intends to fill the time gap between the IRAS, COBE and the follow-on projects SIRTF, FIRST, and PLANK. If it succeeds, it can provide information on research targets for these projects as well as test/resolve some technological issues needed to build these telescopes.

The uniqueness of the proposed telescope lies in the deep cooling of the entire telescope and the even deeper cooling of the detectors to achieve a high sensitivity in submillimeter wavelengths. Comparative sensitivity of the flown projects (IRAS and COBE) and projects under development (SIRTF, FIRST, PLANK) and the Sumillimetron telescope are given in figures 1 and 2.

Figure 1. The sensitivity related to discrete sources.

Figure 2. The sensitivity related to brightness of extended sources.

2. Telescope concept

The telescope will be positioned on the Russian Segment of the International Space Station (Fig.3). The telescope assembly will be oriented in such a way as to preclude interference from the thermal radiation of the station elements, the Sun and the Earth. The angle between the optical axis of the telescope and the directions to these objects will be larger than 60 degrees in all possible telescope pointing positions.

The data registration and processing block will be located in one of the scientific modules of the station and connected with the telescope assembly by a cable.
 
 

---

Figure 3. International Space Station. Top view.

Diameter: D=0.6 m
Focal length: F=4 m

Wavelengths:
- submillimeter band: 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.5 mm
- infrared band: 3, 10, 30, 100, 200 mkm

Cooling:
- telescope as a whole: 5K
- detectors: 0.1K

Detectors:
- bolometer arrays
Number of elements in the detector arrays:
- about 100 at wavelengths shorter than 0.5 mm
- 7 elements at the wavelength 1.5 mm

Angular resolution:
- submillimeter band: 5-20 min of arc
- infrared band: 5 min of arc

Sensitivity of the detectors:

- submillimeter band: 10^-18 W/Hz^1/2

- infrared band: 10E^-17 - 3x10^-16 W/Hz^1/2

Sensitivity of the telescope (integration time = 1 s)
- submillimeter band: 3-12 mJy
- infrared band: 6-40 mJy

Figure 4. Block diagram of Cryogenic Telescope.

Cryogenic Telescope (see Fig. 4) includes following main units:

Technical Requirements on Active Cryogenic System (ACS):

- Load temperature = 20 K.
- Minimum heat load = 1 W.
- Power consumption = 300 W.
- Maximum mass = 30 kg.
- Power voltage = 23-34 V.

Technical Requirements on Star Tracker (STR)

- Accuracy of the telescope pointing axe = ± 10 arc sec.
- Accuracy of the field of view orientaton = ± 1 deg
- Telescope pointing data rate = 1 point per 10 sec.
- Power consumption = 10 W.
- Maximum mass = 10 Kg.

3. Bolometric array concept

Wavelengths: 0.3, 0.4, 0.5, 0.6, 0.8, 1, 1.5 mm.
Bandwidth: 10 - 30% of the observing frequency.
Number of elements in the bolometer arrays:
- about 100 at wavelengths 0.3 - 0.4 mm,
- 7 elements at the wavelength 1.5 mm.
Sensitivity of the bolometers: 10^-18 W/Hz^1/2.

The last figure corresponds to measure of fluctuations in number of quanta in background radiation and can be achieved only with thermal detector (bolometer). For phase sensitive receiver (heterodine mixer) in accordance to indefinity principle the noise temperature is restricted by a value about hv/k. The needed sensitivity can be achieved with extremely low-temperature (about 0.1K) bolometer [1] using Andreev reflection effect [2].
 

4. Possible Participants

Possible Participants of the Submillimetron project are : Astro Space Center (ASC), Russia - project management, scientific program;

Jet Propulsion Laboratory (JPL), USA - active cooling system (ACS), infrared detectors (IDA), test bed;

Chalmers University (CTH), Sweden, Institute of Radio Engineering and Electronics (IREE), Russia - submillimeter bolometers;

P.L.Kapiza Institute of Physical Problems, (KIPP) , Russia - low temperature cooler (mKC);

S.P.Korolev Russian Space Corporation “Energia” (RSC), Russia - payload integration, delivery on orbit;

Space Research Institute (IKI) , Russia - pointing system (TPS).

References

[2] Andreev, A.F., 1964. JETP, 46, p.1283.