Single dish radio telescopes!Is there a need to grow? !Is there a limit to growth?

Development of (sub)-millimeter telescopes!Jacob W.M. Baars!

Max-Planck-Institute for Radio Astronomy!Bonn, Germany!

and!Ideas for future large reflectors ©!

Hans J. Kärcher!© MT-Mechatronics!

Mainz, Germany

1

NRO-ALMA Science/Development Workshop 2015!Nobeyama, 28-30 July 2025

The maximum signal moved in azimuth angle by about four minutes of time per day andJansky correctly concluded that the origin of the noise was located outside the solar system. Heidentified it as cosmic noise coming from the direction of the center of our Milky Way (Jansky,1933). This first radio telescope was nicknamed Jansky's merry-go-round and its azimuthmechanism is the first appearance of a mechanical component still used in modern radio tele-scopes, usually called the wheel-on-track configuration. Jansky proposed the construction of alarge radio telescope, but this was not granted and his bosses moved him to other work in the mid1930s.

ü 3.1.2. Reber’s transit paraboloidal reflectorJansky’s discovery did not create a reaction from the astronomical community, but another

radio engineer and ham-amateur, Grote Reber (1911-2002) was inspired by it. In his backyard inWeaton, Illinois, he built the first sizable and publicly visible parabolic reflector of 9.6 mdiameter with a focal ratio of 0.6, shown in Figure 3.2. Believing that the radiation was of thermalorigin he made his first observations at the highest available frequency of about 3 GHz (10 cmwavelength) at that time (1937). But he did not detect any signal. His next experiment at 910MHz also failed to produce a result, so he finally settled at 160 MHz (wavelength 1.9 m) andthere he was successful. Thus after Jansky's original discovery, radio astronomy was put on asolid footing with the first maps of galactic radio emission collected by Reber (1940). He workedthroughout the war and published several papers with his observations. These indicated that thedominant radiation at radio wavelengths was not of thermal origin, but rather showed a spectralbehaviour of being stronger at longer wavelengths. This component of radiation was totallyunknown at visible wavelengths and its origin, synchrotron radiation from free electrons spiralingin the magnetic field of the Galaxy, was described theoretically only in the early fifties byKiepenheuer (1950) and Shklovski (1951) on the basis of the new radio observations.

Fig. 3.2. Left: the 9.6 m diameter parabolic transit reflector built by Grote Reber in his backyard in Wheaton, Illinois in 1936-37. Right: Reber standing next to his

antenna at the entrance of the National Radio Astronomy Observatory in Green Bank. West Virginia. An azimuth track has been added for full movement.

The structural design of Reber's antenna is astonishingly modern, with a rocking chair conceptfor the elevation section, used in a very similar manner in current extremely large opticaltelescopes designs (as the 30m TMT and the 39m E-ELT). The rotating elevation structure can bedivided in three subsystems: (1) the reflector, (2) the elevation cradle, and (3) the quadripod. Thesystem design is excellent and excites the admiration of a modern structural engineer. It ismiraculous how Reber conceived of his design ideas, particularly when we look at the evolutionof later large radio telescopes, where sometimes detours were taken that proved to be unsuitable.

The original telescope was a transit instrument rotating only in elevation, and was equippedwith a cavity drum receiver at the focus (visible in Fig. 3.2). Reber donated his telescope in the1960s to NRAO in Green Bank, where it was re-installed under his supervision on an azimuthturntable (Fig. 3.2)). Visible is also a service tower for the installation and maintenance work atthe receiver on top of the quadripod. It is an amazingly good design!

3.1. Early history of radio telescopes 27

3.1. Early history of radio telescopes

In 1904 in Germany Christian Hülsmeyer used a close copy of Hertz's apparatus to demon-strate the reception of radiation reflected from a ship, thereby introducing a first primitive versionof radar, albeit without range information. In the early years of the twentieth century the inge-nious inventor Guglielmo Marconi (1874-1937) was instrumental in the development of radiocommunication and broadcasting at long wavelengths, deca- and hecto-meters. The antennas werewire dipoles. In the early 1930s Marconi used parabolic dishes of 3 m diameter in a demonstra-tion of telephony across the English Channel at a frequency near 1.7 GHz. Radar was developedin several countries in the late thirties and was put to use intensely in World War II, usingparaboloidal reflectors at the shorter, decimeter, wavelengths. Great secrecy surrounded theseactivities.

ü 3.1.1. Jansky’s “Bruce” antenna

The major activity in radio however was the emergence of short-wave intercontinentalcommunication, typically at wavelengths of the order of 10 m. It was soon discovered thatweather phenomena, in particular remote thunder-storms, could interfere with the communication.At the Bell Telephones Laboratories in Holmdel, New Jersey, USA, physicist-engineer Karl G.Jansky (1905-1950) was given the task to systematically determine the occurrence of suchinterference as function of time and direction. In 1932 he constructed a so-called Bruce antennafor 14.6 m wavelength (Fig. 3.1) and placed it on a platform, which rotated in azimuth to identifythe direction of any interference. In the process of his experiment he noticed the daily appearanceof a significant increase in the noise level of the receiver.

Fig. 3.1. Karl Jansky in front of his merry-go-round antenna 1932 at the Bell Labsin Holmdel, New Jersey. A copy of the antenna is located at the entrance of the

National Radio Astronomy Observatory in Green Bank, West Virginia, USA.

The maximum signal moved in azimuth angle by about four minutes of time per day andJansky correctly concluded that the origin of the noise was located outside the solar system. Heidentified it as cosmic noise coming from the direction of the center of our Milky Way (Jansky,1933). This first radio telescope was nicknamed Jansky's merry-go-round and its azimuthmechanism is the first appearance of a mechanical component still used in modern radio tele-scopes, usually called the wheel-on-track configuration. Jansky proposed the construction of alarge radio telescope, but this was not granted and his bosses moved him to other work in the mid1930s.

26 The birth of radio astronomy

�".3+9?3��&4&$4*/.�/'��","$4*$��"%*/�!"6&3 The antenna was rotated once every 20 minutes and produced a peak

signal which was fixed in space in the direction of the center of our Milky Way galaxy

17-Sep-11 3 Weinreb Jansky 2011

Beginning of Radio Astronomy - Instrument and Observation

Jansky’s Bruce Antenna at Holmdel!Sep. 1932 - signal trace of !9 revolutions of the antenna Reber’s home-made dish (10 m)!

Maps of the Galactic plane with a!few strong discrete sources (1940)

2

The structural design of Reber's antenna is astonishingly modern, with a rocking chair conceptfor the elevation section, used in a very similar manner in current extremely large opticaltelescopes designs (as the 30m TMT and the 39m E-ELT). The rotating elevation structure can bedivided in three subsystems: (1) the reflector, (2) the elevation cradle, and (3) the quadripod. Thesystem design is excellent and excites the admiration of a modern structural engineer. It ismiraculous how Reber conceived of his design ideas, particularly when we look at the evolutionof later large radio telescopes, where sometimes detours were taken that proved to be unsuitable.

The original telescope was a transit instrument rotating only in elevation, and was equippedwith a cavity drum receiver at the focus (visible in Fig. 3.2). Reber donated his telescope in the1960s to NRAO in Green Bank, where it was re-installed under his supervision on an azimuthturntable (Fig. 3.2)). Visible is also a service tower for the installation and maintenance work atthe receiver on top of the quadripod. It is an amazingly good design!

ü 3.1.3. “Würzburg Riese” radar antennaDuring WW II many parabolic dishes were deployed for radar, both on ships and on the

ground. At the retreat of the German army in the spring of 1945 the European Atlantic coast wasdotted with radar antennas of 7.5 m diameter, called Würzburg Riese. The German word 'Riese'means giant and it is indicative of the state of the art in parabolic reflectors at that time. Several ofthe antennas were ‘adopted’ by radio astronomy groups in statu nascendi in England, France,Scandinavia, the USA and the Netherlands. If the antenna was in good condition, one could use itat wavelengths as short as 10-20 cm. Figure 3.3 shows the Dutch Würzburg antenna, located atthe short-wave transmitting station in Kootwijk. This antenna was used for the first extensivemapping of the distribution of neutral hydrogen atoms in our galaxy at a wavelength of 21 cm.This spectral line had been predicted to be observable by Henk van de Hulst (1918-2000) during awar-time colloquium in Leiden in April 1944, and was detected in 1951 at Harvard University byEwen and Purcell (1951), 6 weeks later confirmed in Kootwijk by Muller and Oort (1951) andshortly afterwards from Australia by Christiansen and Hindman (1952).

Fig. 3.3. A ‘Würzburg Riese” German radar antenna of 7.5 m diameter, relocated after the War to the Kootwijk radio transmitting station (see the antenna masts in the left background), with

which the 21 cm hyperfine line of neutral hydrogen in our Galaxy was detected in 1951.

Depending on the major observing program for the antennas, they were used with differenttypes of mount (Fig. 3.4). The Dutch group used the original alt-azimuth mount of the radarantenna, whereas a US team of solar physicists at the National Bureau of Standards changed to anequatorial mount to ease sidereal tracking of the Sun, thereby avoiding painstaking coordinatetransformations. The group in Cambridge, UK concentrated on sky surveys and reduced theantenna to a transit instrument. The three examples give some hints to the importance of thetelescope mount and its complexity from the mechanical and structural engineer's point of view.We discuss this more fully in later chapters.

28 The birth of radio astronomy

Detection of the 21-cm neutral hydrogen line - 1951

WWII radar antenna in Holland and the first !published line spectra by Muller and Oort

Horn antenna at Harvard with published!observation by Ewen and Purcell3

Serendipitous discoveries in radio astronomy

< <Lunar occultation 3C273, ! Hazard, Schmidt 1963!!CO-line at 115 GHz, >>!Wilson, Jefferts, Penzias1970 !!CMB, Penzias, Wilson, 1965 V! V!!V Pulsar, Bell, Hewish, 1967

4

1. The most important observational discoveries result from substantial technological innovation. Still true!

2. Once a powerful new technique is applied, the most profound discoveries follow with little delay. Probably still trueThis results in a new instrument soon exhausting its capacity for discovery. Doubtful. It better not apply to ALMA!!

3. Observational discoveries of new phenomena frequently occur by chance. Still true, but more rareAbout half the cosmic phenomena now known (1980) were chance discoveries. Many of these were discovered by individuals who designed and built (“owned”) the equipment. Few originated at “national observatories”. This has changed significantly with the big synthesis telescopes. VLA, IRAM, ALMA, SKA and Space Telescopes are beyond the capacity of individual, university-type institutes. They are now multinational collaborations.

Statements in “Cosmic Discovery” !by Martin Harwit in 1980

5

Major telescope parameters

• Science - sensitivity (S, Tb) and angular resolution!

• Engineering - Surface precision Pointing accuracy and stability Beam shape (sidelobe level)!

• Environment - Gravity effectsTemperature and wind influencesAtmospheric conditions - water vapour, clouds

6

The basic requirements of a radio telescope

Sensitivity - Collecting area, reflector surface precision!Angular resolution - Linear size and axes control!!Surface accuracy better than λ/20 (for 75% efficiency)!Pointing accuracy and stability better than 0.1 HPBW

Diam. (m) Min. λ (mm) HPBW (“) Surf. (µm) Example12 0.32 6.5 14 20 ALMA25 0.2 2.0 8.5 12? CCAT40 0.2 1.0 8.5 future?50 1.2 6.0 51 75 LMT80 1.0 3.0 43 future?

100 3.5 8.5 150 400 Eff./GBT

Examples with required (black) and achieved (red) surface

7

Natural limits for steerable radio telescopes Sebastian von Hoerner, !

“Design of large steerable antennas”, 1967

8

Natural limits: Gravity - λg ≈ 70 ( D/100)2, Thermal λt ≈ 6 ΔT (D/100) ! (D in meter and wavelength in millimeter, temperature in Kelvin)

9

To go beyond the natural limits requires new, non-classical design methods (homology) and/or additional actions like thermal insulation, new materials (CFRP), active optics

The designs are different in three points: 1) the diameter of the elevation wheel of the Krupp design is much larger than that of the

MAN; 2) the quadripod for the secondary is in the MAN design attached to the backup structure; in

the Krupp design it is attached to the octahedron completely separate from the backup structure; 3) the MAN design has an elevated azimuth track, resting on a circular three-story building.

Hachenberg’s evaluation report discloses that the final reflector deviations of the MAN designwere twice that of the Krupp design, which was due to its much more sophisticated supportingsystem for the quadripod. In the MAN design the loads of the quadripod could not be distributedin the BUS in a homologous way, leading to a higher rms reflector deviation. Hachenberg wasconvinced by Altmann’s design as summarised by him in his evaluation report. The intelligenceof this design and the resulting better reflector accuracy gave him the decisive argument for thechoice of the Krupp solution. A somewhat complete impression of the telescope structure isshown in Fig. 5.13.

Fig. 5.13. The three basic building blocks and a cross section through the Effelsberg telescope

The realization of Hachenberg’s dream went very smooth. The Volkswagen Stiftung grantedthe money for the 100 m version, and the competing companies were persuaded to form a jointventure (ARGE Star) with Krupp as leader for design and manufacture, and MAN leading the on-site assembly and erection. The 100-m telescope was inaugurated on May 19, 1971 (Fig. 5.14)and a description with measured system parameters appeared in 1973 (Hachenberg et al., 1973).

5.4 The 100-m Effelsberg telescope of MPIfR 87

Homology design - Effelsberg 100-m telescope (1971)

10

Homologous behaviour transfers the shape of the reflector to equally accurate paraboloids as function of elevation angle with a computable change in focus position (axis direction and focal length). The feed/subreflector must be adjusted to this “moving” focus during observation. A homology telescope has more than an order of magnitude better surface accuracy than a “classical” design, while weighing much less.

Only points B of the blue “umbrella” reflector structure are connected to the red octahedron elevation structure at B.!The octahedron is supported by the black alidade at the elevation bearings A. The quadripod is part of the octahedron and does not touch the reflector at all.

Progress in Design and Fabrication since 1970

1. Continuous improvements in the precision of structural design optimisation (FEA)!2. Optimum choice of structural materials (CFRP)!3. Improved manufacturing methods, specifically surface panels, bearings.!4. Sophisticated servo-control methods and hardware, algorithms, encoders, drives!5. Application of “active optics”, motor-controlled surface actuators, using FEA data!5. Improvements in the measurement and setting of the reflector surface, holography!6. Active thermal control of structural elements!!7. Flexible Body Control(FBC) for improved pointing with sensors (tilt meter, pressure gauge, temperature sensor, displacement sensor)

11

Examples of large radio telescopes with passive surface

IRAM 30m MRT !Pico Veleta Spain

• First light 1983!• 30 m main reflector diameter!• Yoke type support system!• 70 µm rms surface accuracy!• Outside insulated cladding!• Active temperature control!• Passive optics

IGN 40m !Yebes Spain

• First light 2005!• 40 m main reflector diameter!• Yoke type support system!• 220 µm rms surface accuracy!• Outside cladding!• Temperature control:

forced ventilation!• Provisions for active optics

(open loop, not yet installed)

MPIfR 100m Effelsberg!Bonn Germany

• First light 1972!• 100 m main reflector diameter!• Centrally suspended

homologous reflector!• Perforated outer reflector rim!• 400 µm rms overall surface accuracy (passive, solid surface)!• Temperature control;

white painting!• Active subreflector 2005

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Examples of large radio telescopes with active surface LMT/GMT 50 m !

Cerro la Negra Mexico

• First light 2011!• 50 m main reflector diameter!• Yoke type support system!• 75 µm rms overall !• surface accuracy (goal)!• Outside cladding!• Temperature control via

forced ventilation!• Active optics (open loop)!

SRT 64 m INAF !San Basilio Sardinia

• First light 2012!• 64 m main reflector diameter!• Centrally suspended, semi-

homologous reflector!• 200 µm rms overall surface

accuracy!• Provisions for outside cladding!• Provisions for forced ventilation!• Active optics (open loop)

100-110 m GBT !Green Bank USA

• First light 2000!• 100-110 m off-set main reflector!• Centrally suspended !• non-homologous reflector!• Off-set subreflector!•200 µm rms surface accuracy goal!• Active optics (open loop)!• Temperature control: white paint!• Closed loop surface control goal13

Weight comparison per collecting area

MRT IGN Effelsb LMT SRT GBT/d GBT/b

Diameter (m) 30 40 100 50 64 102 102

Precision (µm) 70 220 400 75 220 200 200

Active surface no no no yes yes yes yes

Total weight (ton) 732 764 3165 2980 3150 5557 7400

Surface weight /m 56 33 32 100 33 31 31

Bus weight /m 134 138 87 190 181 125 175

Elev. Str./m 215 147 73 185 115 150 200

Alidade /m 212 175 117 688 358 272 363

Overall weight/m 1036 608 403 1518 979 694 924

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Last row: note high numbers for MRT and LMT and very low value for Effelsberg, less than half of GBT

Design and Technological Progress!Overcoming Natural Limits

Design: Homology, FEA, Thermal analysis - ! ! ! ! Effelsberg, MRT, ALMA!!Materials: CFRP - Backup Structure - ! ! ! ! ! ! ! IRAM, HHT, ALMA! ! ! ! ! Panels - ! ! ! ! ! ! ! ! ! IRAM, NRO, HHT!!Fabrication: Surface panels - machined aluminium - small, 4 µm; ! ! APEX, ALMA!! replica from mold - aluminium composite - large, 10-25 µm, ! ! MRT, JCMT!! ! ! ! ! - CFRP/Alu composite - large, 5 µm. ! ! ! ! ! HHT - electro-formed nickel/alu composite - medium to large, 5-10 µm,!! ALMA, LMT!!Active Optics: gravitational surface correction by actuators based on FEA - LMT, GBT! - thermal surface correction by temperature measurement and FEA - MRT, LMT, GBT!!Thermal control: active temperature equalisation system - ! ! ! ! ! MRT!!Flexible Body Control: pointing/tracking - tilt meter, displacement sensor ALMA, LMT!!Reflector measurement/setting: photogrammetry (30 µm), holography (10 µm) - ALL!!

15

16

Temperature effects!the second natural limit

- Asymmetric temperature distribution in structure!- Time dependent difference between structural

sections with different thermal time constant!- Temperature gradients, possibly time-variable, in

structure and reflector panels

Possible Actions!!- Insulation of structural members!- Forced air circulation in structure!- Active temperature control with heating/cooling system!- Measure temperature distribution and correct via FEM!- Use of material with low thermal expansion (CFRP)!- Restrict observations to night-time

17

Temperature effects and their Control in the IRAM 30-m

mm-telescope

In the 30-m telescope the BUS and Quadripod are actively controlled to equal the temperature of the Yoke

Focus changes by 1 mm when Yoke and BUS temperature differ by 1 K; corrected in real time

Temperature gradient in BUS of 1K will cause 10 µm surface error. 5 K or more can happen during daytime from the Sun.

New Technologies and Materials!Carbon fiber reinforced plastic (CFRP)

HHT on Mt.Graham, Arizona - 10 m diameter!(1993). BUS truss of CFRP tubes, invar steel nodes. Thermally essentially inert. High stiffness to weight ratio. Gravitational deformation <3 µm.!Overall surface precision 12 µm.

IRAM on Pl. de Bure, France !15 m diameter (1988). BUS mixture of steel and CFRP. Overall precision 50 µm.

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CSO IRAM HHT ALMA-NA

ALMA-EU

CCAT-spec.

Diameter (m) 10.4 15 10 12 12 25

Precision (µm) 17 50 12 20 20 12.5

Panels alu cfrp cfrp alu ni/alu alu

BUS steel cfrp/steel cfrp/invar cfrp/alum cfrp cfrp

Elevation steel steel steel steel cfrp cfrp

Thermal control some no no some no no

Active surface yes no no no no yes

FBC/pointing no no no yes yes yes

Year 1986 1988 1993 2010 2010 design!study

Parameters of some submillimeter radio telescopes

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20

Wind Effects!Time- and Direction-Dependent!

- Wind causes Surface deformation and Pointing variations, varying quickly in time!

- Wind has constant and gusty component and its angle of attack is variable

- Major influence on Pointing stability/accuracy!- Can cause pointing errors not detected by angle encoders!- Correct with sensors on structure via FEA (finite

element analysis) and FBC (flexible body control)!- Sensors include inclinometer, linear displacement sensor,

accelerometer, pressure gauge!- Surface deterioration normally of secondary importance;

difficult to measure and correct

Active controlled Optics

Ref

lect

ors

/ Rec

eive

rs

Main AxesDrives

Main AxesEncoders

PositionController

FBCModel

PositionCommands

Desired Pos.

ActualPos.

SubreflectorPositioner

SurfaceAdjusters

Alidade Inclin. & others

TemperatureSensors

Deform.Status

Str

uct

ure

&M

ech

anic

s

ImageQuality

Controller

Ast

ron.

Tar

get

-

Open loop “active optics” for radio telescopes!FBC - Flexible Body Control!

FEA - Finite Element Analysis

Deformation status

FEA - focus, surface

Pointing correction

FEA

21

22

Large single Dish !or!

Interferometric Array?

NRO and IRAM have both! - 1980s!!

ALMA, plus ACA - 2012

NRO

IRAM

ALMA

Timeline and growth of Millimeter Telescopes!(pictures about to scale)

NRAO - 1968 - 11 m!IRAM - 1985 - 30 m!NRO - 1982 - 45 m!LMT - 2015 - 50 m!VLMT - ?? - 80 m ?

NRAO

NRO LMT

VLMT!©MTM

© MT Mechatronics GmbH 2015 - Kärcher

Ideas for future large reflectors

19.07.2015 2

VLMTVery Large Millimeter Telescope

• Reflector 80 m

• Surface accuracy

• 60 µm rms overall

• 20 µm rms inner 40m

• Frequency range

• <300 GHz overall

• <1000 GHz inner 40m

80m

IRAM

23

wavelength!1 mm

size (m)!number

surface!area (m

resolution!(arcsec)

sensitivity!(rel. point s.)

NAOJ 45 1

1600 ( - )

6 -

IRAM-PV 30 1

700 (350)

8 0.8

LMT 50 1

1960 (800)

5 1.7

CCAT 25 1

490 (470)

10 1.0

NOEMA 15 12

2100 (52) (1400, 42)

0.3 2.8

ALMA 12 50

5700 (85) (5400, 83)

0.02 11

ACA 7 + 12 12 + 4

910 (34) (880, 33)

7 1.8

SMA 6 8

225 (17) (220, 16.5)

0.4 0.5

Comparison of (sub)mm telescopes

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- Blue numbers refer to 1 mm wavelength. Array area equivalent diameter in brackets!- ALMA is vastly superior in sensitivity and angular resolution!- ACA is equivalent to 33 m single dish with full sensitivity in submm, almost twice that of CCAT

Ideas for future large radio telescopes

VLMT Very Large Millimeter Telescope

VLTHT !Very Large Tera Hertz Telescope

OWLRT Extremely Large Radio Telescope

Standard passive surface

Open loop flexible body control

Closed loop shape control

Low cost

New concepts based on rough extrapolation by Hans Kärcher!design concepts © MT Mechatronics GmbH

12 29.04.2014 Kärcher

With the above explained methods for accuracy enhancement it may be possible to shift the accuracy limit (yellow line in the diagram) one order of magnitude above the accuracy of the “standard”  passive  telescope  (magenta  line  in  the  diagram). Some deliberation of the situation according this diagram leads to the proposal of three new diameter/frequency regimes, which are up to now not covered by existing telescopes:

1. A Very Large Terahertz Telescope VLTHT with a main reflector diameter of 40m and a frequency range up to 2 THz.

2. A Very Large Millimeter Telescope VLMT with 80m main reflector diameter and a frequency range up to 300 GHz.

3. A low cost Overwhelming Large Radio Telescope OWLRT with a main reflector diameter of 160m and a frequency range of 2 GHz.

The feasibility of these three projects is shown by the above given explanations and diagrams from the engineering point of view. Their justification from the science point of view has to be developed by scientist via an appropriate description  of  an  adequate  “science  case”.  

10m1m1mm1µm

1.0

10.0

100.0

1,000.0

100m

1000m

EffelsbergGBT

LMT IGN

MRT

IRAM

ALMA

Arecibo

FAST

ParkesSRT

MERLIN

σ

D

GMRT

SKA

300-ft

CCAT

VLMT

OWLRT

VLTHT

Future large radio telescopes –not yet built!

VLMT Very Large Millimeter Telescope

• Reflector � 80m• Surface accuracy 60µm• Frequency range <300 GHz

VLTHT Very Large Tera Hertz Telescope

• Reflector � 40m• Surface accuracy 10µm• Frequency range <2 THz

OWLRT Overwhelming Large Radio Telescope

• Reflector � 160m• Surface accuracy 10mm• Frequency range <2 GHz

• Reflector ∅ 40 m!• Surface accuracy 10 µm!• Frequency range <2 THz

• Reflector ∅ 80 m!• Surface accuracy 60 µm!• Frequency range <300 GHz

• Reflector ∅ 160 m!• Surface accuracy 5 mm!• Frequency range < 4 GHz

..

.SKA

ALMA

25

NOEMA

© MT Mechatronics GmbH 2015 - Kärcher

Ideas for future large reflectors

19.07.2015 1

40m

80m

90m40m

VLTHTVery Large Tera Hertz Telescope

• Reflector 40 m

• Surface accuracy 10 µm rms

• Frequency range <2 THz

26

Basic Features!- BUS and Elevation structure in CFRP!- Homologous structure!- Closed-loop Active Surface (Keck-type ?)!- FBC with advanced sensors!- “Seeing” (anomalous refraction) correction

system operational!- Dome for survival and wind protection

© MT Mechatronics

© MT Mechatronics GmbH 2015 - Kärcher

Ideas for future large reflectors

19.07.2015 2

VLMTVery Large Millimeter Telescope

• Reflector 80 m

• Surface accuracy

• 60 µm rms overall

• 20 µm rms inner 40m

• Frequency range

• <300 GHz overall

• <1000 GHz inner 40m

80m

27

unlikely

( )?

Basic Features!- BUS and Elevation structure in CFRP!- Homologous “Effelsberg-type” structure!- Closed-loop Active Surface (tip-tilt sensor/actuator)!- FBC with advanced sensors!- “Seeing” (anomalous refraction) correction system operational

© MT Mechatronics

OWLRT !Overwhelming Large Radio Telescope!

(a “desk exercise”)

• Reflector ∅ 160 m!• Wire mesh surface possible!• Surface accuracy 5 mm!• Frequency range < 4 GHz

180m Sugar Grove 1966

Transition to “rocking chair” concept

39m E-ELT 2010

28

Not a realistic alternative to Square Kilometre Telescope (SKA)

© MT Mechatronics

MT Mechatronics design and concept validation study for ESO

Single dish millimeter radio telescopes!!

Is there a need to grow? !I am not convinced there is!!

!Is there a limit to growth?!

There is, and we are approaching that limit!both in technology and funding

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