Fregat upper stage

Entering service at the turn of the 21st century, the Fregat (frigate) became the main fourth stage for the Soyuz family of rockets flying from four launch sites around the world. The Fregat was also adapted as a third stage of the Zenit rocket for some of its most critical missions.

The high-performance Fregat space tug originated as a propulsion stage for the Soviet Mars probes. It was later adapted for many deep-space missions, thanks to its ability to fire its engine multiple times and function in space for prolonged periods.

Technical specifications of the Fregat upper stage (118; 207):

Fueled mass
6,415 - 6,535 kilograms (Fregat-MT: 7.5 tons)
Dry mass
980 - 1,100 kilograms
Height 1,500 millimeters
Diameter 3,350 millimeters
Fuel UDMH (Unsymmetrical dimethyl hydrazine)
Oxidizer NTO (Nitrogen tetroxide)
Maximum propellant load for main engine 5,350 kilograms
Main engine S5.92
Thrust 2,000 kilograms
Specific impulse 327 - 328.5 seconds
Number of engine firings up to 20
Propellant load (one component: hydrazine) for the attitude control system, RSU 85 kilograms (in 2012 reported as 63 kilograms)
Number of attitude control thrusters 12
Thrust of attitude control engines 5 kilograms
Specific impulse of the attitude control system 225 seconds

Formally, the development of the Fregat upper stage started around 1991 or 1992 in conjunction with the Rus project, envisioning a series of upgrades of the Soyuz rocket family. The Fregat was expected to serve as a fourth (upper) stage for the Soyuz-2 rocket, delivering payloads from low "parking" orbits into various high-altitude orbits or sending planetary probes into deep space. Potentially, Fregat could be adapted to serve as the third stage of the Soyuz rocket, instead of Block I stage, to form the Vostok-2/Fregat booster. In such configuration, the rocket could launch cargo into low- and mid-altitude orbits, as well as into sun-synchronous orbits.

Finally, Fregat could become the third stage of the Zenit rocket, or the fifth stage of the Proton M/Block D combination. When combined with Block D onboard the Proton, Fregat could deliver 3,500 kilograms of payload into geostationary orbit, compared to 2,600 kilograms without it.

NPO Lavochkin claimed that Fregat's performance characteristics would exceed those of any contemporary vehicle. The stage inherited many of its components from previous Soviet hardware, reducing the development cost and increasing the overall reliability of the system.

Design features

Fregat

The Fregat's exotic architecture traces its roots in the Soviet lunar probes developed at NPO Lavochkin in the 1960s. The stage is made up of six overlapping spherical sections, only four of which serve as propellant tanks. Two remaining spheres are actually instrument sections, one containing unpressurized avionics, which can function in vacuum of space and another, pressurized, section holding a flight control computer, which requires a temperature-controlled environment.

At least four spherical gas tanks with a diameter of 375 millimeters and a capacity of 23 liters are carried onboard Fregat.

The main propulsion unit of the Fregat upper stage consists of a single S5.92 engine. Capable of multiple firings and dual-thrust mode, it uses a turbo-pump and operates in a gas-generator cycle. The stage has also a single-component attitude control system, SOiZ, which has its own propellant cache of between 63 and 85 kilograms of hydrazine. The small engines of the SOiZ system have a thrust of five kilograms and specific impulse of 225 seconds.

The "flat" architecture of Fregat allowes to minimize its mass and the inertia to be overcome during engine firings. As a result, developers can place the main engine of the ADU on special rail guides instead of a gimbal mechanism in order to steer the thrust of the propulsion system.

Technical specifications of the S5.92 engine used on Fregat upper stage (340):

Thrust in vacuum
1,400 kilograms and 2,000 kilograms
Specific Impulse
323 seconds and 329 seconds
Propellant component ratio
2.05 and 1.95
Thrust development time (to 90 percent from nominal)
2.5 - 3.0 seconds
Duration of firing
1,350 seconds
Restart capability
25 times
Engine gimbal capability (yaw and pitch)
±300 millimeters
Engine dry mass
75 kilograms
Engine dimensions
677 x 838 x 1,028 millimeters
Life span in orbit
Three years

Fregat variants

Fregat SB

NPO Lavochkin also proposed the Fregat-2 version of the upper stage, equipped with a jettisonable external tank. If lifted by the Zenit rocket, the Fregat-2 could deliver 2,300 kilograms of payload into geostationary orbit, while in combination with the Proton M rocket, 4,000 kilograms could be inserted into the same orbit. (118) The vehicle was later renamed Fregat-SB, where SB stands for "sbrasyvaemye baki" or "jettisonable tanks," and its first mission was scheduled to be the launch of the Spektr-R scientific satellite onboard a Zenit-3M rocket. Routine preflight processing of the vehicle was planned at the assembly building at Site 31 in Baikonur.

Fregat-M/Fregat-MT

Yet another unique modification of the Fregat upper stage was developed specifically for the Phobos-Grunt mission. It was dubbed Flagman and it also featured a jettisonable external tank, as well as additional ball-shaped inserts on the upper hemispheres of the propellant tanks. Similar tank extensions were added to the particular versions of Fregat meant to fly on the Soyuz-ST rocket from Kourou, such as those intended to carry Europe's Galileo navigation satellites. This version of the stage was identified as Fregat-MT. According to unofficial sources, propellant tank inserts enabled to increase the propellant load from 5,350 kilograms to 6,640 kilograms, without any changes in the critical physical dimensions of the vehicle. In the meantime, Arianespace officials confirmed that some preliminary consideration had been given to equipping Europe's flagship Ariane-5 rocket with Fregat in order to fly trajectories, which would require multiple firings of an upper stage in space.

Fregat-SBU

During an expanded session of the Scientific and Technical Council, NTS, on May 29, 2018, Sergei Ishin, Deputy Designer General, presented plans for the Fregat-SBU variant, which would be adapted for the Soyuz-5 and Angara-3 launch vehicles. According to NPO Lavochkin, the council approved the development of the Fregat-SBU variant.

Flagman

At the turn of the 21st century, NPO Lavochkin considered the Flagman two-stage space tug, which would combine the 11S824M upper stage (Block-D) and Fregat, serving as the second stage. The combo was apparently intended for placing satellites directly into the geostationary orbit, GSO. The space tug could deliver 3,100 kilograms of cargo on the Proton rocket or 3,500 kilograms either on Proton-M flying from Baikonur or an Angara-5 rocket based in Plesetsk.

 

Fregat-M/Fregat-MT specifications (410):

-
Fregat-M
Fregat-MT
Total (dry) mass
920 kilograms
1,030 kilograms
Maximum propellant load
5,250 kilograms
6,550 kilograms
Height
1.55 meters
-
Maximum diameter
3.35 meters
3.38 meters
Engine thrust (high-thrust mode)
2,000 kilograms
-
Engine thrust (low-thrust mode)
1,400 kilograms
-
Specific impulse
333.2 seconds
-
Number of possible engine firings
7
-

In-flight problems

In 2012, posters in the Novosti Kosmonavtiki web forum reported that during the mission to deliver the COROT space observatory, the Fregat upper stage had experienced problems. As it transpired, a valve tasked to reduce pressurization of propellant tanks from 320 bars to 38 bars had leaked. As a result, the pressurization system worked below specifications during the mission, failing to provide needed pressure into the propellant tanks during the Fregat maneuvers. Fortunately, it was still enough to deliver propellant for all firings of the main engine and keep the vehicle on the right trajectory. A similar problem took place onboard Fregat during the launch of the Globalstar satellites on May 30, 2007.

The investigation later concluded that specific design of the valve and the loss of flexibility in its membrane had been likely culprits. One source claimed that KBKhM design bureau, which built the Fregat's propulsion system possible used a new materials, later reverted back to previous design, thus solving the problem.

Production rates

In 2011, NPO Lavochkin built 12 Fregat stages, 11 of which were expended during missions. The production of 10 more stages was ordered during 2012, while nine stages were scheduled to fly, including three on the Soyuz rockets from French Guiana. NPO Lavochkin reconfirmed the annual production rate of 12 Fregat stages again in May 2018.

 

A complete list of Fregat missions:

No. Launch date
Payload
Payload type
Launch vehicle
Launch site
Launch complex
Launch pad
Status
1
2000 Feb. 9
Demonstrator, IRDT
Experimental
Soyuz-U
Baikonur
31
6
Success
2
2000 March 20
Dumsat
Experimental
Soyuz
Baikonur
31
6
Success
3
2000 July 16
Cluster-2 (5-6)
Science
Soyuz
Baikonur
31
6
Success
4
2000 Aug. 9
Cluster-2 (7-8)
Science
Soyuz
Baikonur
31
6
Success
5
2003 June 2
Mars Express / Beagle-2
Planetary / Mars
Baikonur
31
6
Success
6
2003 Dec. 28
Amos-2
Application / communications
Soyuz-FG
Baikonur
31
6
Success
7
2005 Aug. 14
Galaxy-14
Application / communications
Soyuz-FG
Baikonur
31
6
Success
8
2005 Nov. 14
Venus-Express
Planetary / Venus
Soyuz-FG
Baikonur
31
6
Success
8
2005 Dec. 28
GSTB-V/2A
Application / navigation
Soyuz-FG
Baikonur
31
6
Success
10
2006 Oct. 19
Application / remote sensing
6
Success
11
2006 Dec. 24
Military / communications
4
Success
12
2006 Dec. 17
Science / astronomy
6
Success
13
2007 May 30
Globalstar (4)
Application / communications
Soyuz-FG
Baikonur
31
6
Success
14
2007 Oct. 21
Globalstar (4)
Application / communications
Soyuz-FG
Baikonur
31
6
Success
15
2007 Dec. 14
Radarsat-2
Application / remote sensing
Soyuz-FG
Baikonur
31
6
Success
16
2008 April 27
GIOVE-B
Application / navigation
Soyuz-FG
Baikonur
31
6
Success
17
2009 May 22
Military / communications
4
Failure*
18
2009 Sept. 17
Meteor-M No. 1
Sterkh-2
BLITS
SumbandilaSat (ZA-002)
Universitetsky-Tatyana-2
UGATUSAT
Iris
Application / remote sensing
31
6
Success
19
2010 Oct. 19
Globalstar-2 (1-6)
Application / communications
31
6
Success
20
2010 Nov. 2
43
4
Success
21
2011 Jan. 20
Application / remote sensing
-
Success
22
2011 Feb. 26
Kosmos-2471 (GLONASS-K1 (No. 11))
Navigation
43
4
Success
23
2011 May 4

Meridian (4)

Military / communications
43
4
Success
24
2011 July 13

Globalstar-2 (6)

Communications
6
Success
25
2011 July 18
Science / astronomy
-
Success
26
2011 Oct. 3
GLONASS-M No. 42 (Kosmos-2474)
Navigation
43
4
Success
27
2011 Oct. 21
Navigation
Soyuz-ST-B
-
Success
28
2011 Nov. 28
GLONASS-M (Kosmos-2478)
Application / navigation
43
4
Success
29
2011 Dec. 17
Military
-
Success
30
2011 Dec. 23
Military / communications
4
Success
31
2011 Dec. 28
Globalstar-2 (13-18)
Applications / Communications
6
Success
32
2012 July 22
Kanopus-V No. 1, BKA, MKA-FKI-PN1, exactView-1, TET-1
6
Success
33
2012 Sept. 17
Application / weather forecasting
6
Success
34
2012 Oct. 12
Application/navigation
-
Success
35
2012 Nov. 14
Military / communications
4
Success
36
2012 Dec. 1
Military / remote-sensing
-
Success
37
2013 Feb. 6

Globalstar-2 (FM19, FM20, FM21, FM22, FM23, FM24)

Application / communications
6
Success
38
2013 April 26
Application / navigation
4
Success
39
2013 June 25
Application / communications
-
Success
40
2013 Dec. 19
-
Success
41
2014 March 24
Military / navigation
4
Success
42
2014 April 3
Application / remote sensing
-
Success
43
2014 June 14
4
Success
44
2014 July 8
Meteor-M No. 2, TechDemoSat-1, SkySat-2, M3MSat mass mockup, MKA-FKI (PN2) Relek, DX1, AISSAT-2, UKube-1
Application / remote sensing
6
Success
45
2014 July 10
Application / communications
-
Success
46
2014 Aug. 22
Application / navigation
-
Failure
47
2014 oct. 30
Military / communications
4
Success
48
2014 Dec. 1
Military / navigation
4
Success
49
2014 Dec. 18
-
Success
50
2015 March 27
Application / navigation
-
Success
51
2015 Sept. 10
Application / navigation
-
Success
52
2015 Nov. 17
Military / early warning
4
Success
53
2015 Dec. 17
Application / navigation
-
Success
54
2015 Dec. 11
Application / remote sensing
-
Success
55
2016 Feb. 7
Military / navigation
4
Success
56
2016 April 25
Application / remote-sensing
-
Success
57
2016 May 24
Application / navigation
-
Success
58
2016 May 29
Military / navigation
4
Success
59
2017 Jan. 27
Application / communications
-
Success
60
2017 May 18
Application / communications
ELS
-
Success
61
2017 May 25
Military / Early warning
-
-
Success
62
2017 July 14

Kanopus-V-IK, Flying Laptop, WNISAT-1R,
TechnoSat,
NORSAT-1, -2,
CICERO 1-3,
Corvus-BC 1 (Landmapper-BC 1, -2),
MKA-N 1-2,
Flock-2k-1 -
Flock-2k-48 (Dove 101C),
Lemur-2 42-
49,
NanoACE,
Mayak, Iskra-MAI-85, Ecuador-UTE-YuZGU

Application / remote-sensing
6
Success
63
2017 Sept. 22
Military / navigation
4
Success
64
2017 Nov. 28
Meteor-M No. 2-1, Baumanets-2, LEO Vantage, AISSat-3, IDEA OSG-1, SEAM, Landmapper-BC-1, Landmapper-BC-2, Lemur-2 (1), Lemur-2 (2), Lemur-2 (3), Lemur-2 (4), Lemur-2 (5), Lemur-2 (6), Lemur-2 (7), Lemur-2 (8), Lemur-2 (9), Lemur-2 (10), D-Star One
Application / remote sensing
-
Failure
65 2017 Dec. 26
Zenit-3SLBF No. SLB80.5/Fregat No. 2006
-
Success
66
2018 Feb. 1
Kanopus-V No. 3, Kanopus-V No. 4, S-Net-1, S-Net-2, S-Net-3, S-Net-4, Lemur-2-Kadi, Lemur-2-Thenickmolo, Lemur-2-Jin-Luen, Lemur-2-Uramchansol, D-StarOne
Application / remote sensing
-
Success
67
2018 March 9
Application / communications
-
Success
68
2018 June 17
Military / navigation
4
Success
69
2018 Nov. 3
Military / navigation
4
Success
70
2018 Nov. 6
Application / meteorology
-
Success
71
2018 Dec. 19
Military / reconnaissance
-
Success
72
2018 Dec. 27
Kanopus-V No. 5, Kanopus-V No. 6, Flock-3k Dove-1-12, ZACube-2, Lume-1, D-Star ONE (iSat), D-Star ONE (Sparrow), Lemur-2-30 - Lemur-2-37-Daisy-Harper, UWE-4
Application / remote sensing
-
Success
73
2019 Feb. 21
Military / observation
6
Success
74
2019 Feb. 27
-
Success
75
2019 April 4
Application / communications
-
Success
76
2019 May 27
Military / navigation
4
Success
77
2019 July 5
Meteor-M No. 2-2, Momentus X1, NSLSat-1, Lemur-2 (100-108), JAISAT-1, EXOCONNECT, D-Star One (Lightsat), Lucky-7, SEAM-2.0, MTCube, SONATE, Beesat-9 - 13, MOVE-2b, TTU-100, Ecuador-UTE, ICEYE-X4, ICEYE-X5, DoT-1, MKA Sokrat, VDNKhA-80, AmurSat (AmGU-1)
Application / remote-sensing
-
Success
78
2019 July 30
4
Success
79
2019 Sept. 26
Military / early warning
4
Success
80
2019 Dec. 11
Military / navigation
3
Success
81
2019 Dec. 18
Millitary / observation
-
Success
82
2020 Feb. 7
Application / communications
6
Success
83
2020 Feb. 20
Military / communications
3

Success

84
2020 March 16
Military / navigation
4
Success
85
2020 March 21

OneWeb (41-74)

Application / communications
6
Success
86
2020 May 22
Military / early warning
4
Success
87
2020 Sept. 28
Gonets-M No. 27, 28, 29, Dekart, Iceye X-6 (2), Kepler-2 (2), LacunaSat-3, Lemur-2y (4), MeznSat, NetSat (4), Norbi, SalSat, Yarilo (2)
Application / communications
-
Success
88
2020 Oct. 25
GLONASS-K No. 15L (Kosmos-2547)
Military / navigation
4
Success
89
2020 Dec. 1
Military / reconnaissance
-
Success
90
2020 Dec. 3
3
Success
91
2020 Dec. 18
Application / communications
-
Success
92
2020 Dec. 29
Military / reconnaissance
-
Success
93
2021 Feb. 28
Application / weather forecasting
6
Success
94
2021 March 22
Application / remote sensing
6
Success
95
2021 March 25
Application / communications
-
Success
96
2021 April 26
Application / communications
-
Success
97
2021 May 28
Application / communications
-
Success
98
2021 July 1
Applications / communications
-
Success
99
2021 Aug. 22
Applications / communications
6
Success
100
2021 Sept. 14
Applications / communications
6
Success

*Spacecraft delivered into an off-nominal orbit

 

Writting, photography and illustrations by Anatoly Zak; Last update: September 15, 2021

Page editor: Alain Chabot; Last edit: March 7, 2011

All rights reserved

insider content

 

Fregat upper stages at NPO Lavochkin's testing and checkout station, KIS. The development and test version is on the foreground, a demo version is on the background. Click to enlarge Copyright © 2001 Anatoly Zak


An original concept of the Fregat-2 upper stage with a jettisonable external tank, which was evaluated around 2001. One proposed version of Fregat would reportedly reach 17 tons. Credit: NPO Lavochkin


Flagman

Project of the Flagman upper stage, which combines Block D and Fregat stages.


Upgrading Soyuz with the off-the-shelf Fregat upper stage would enable it not simply "loop" around the Moon, but enter orbit around the Earth's natural satellite. The Soyuz/Fregat combination could be launched by an upgraded version of the Soyuz rocket. Copyright © 2007 Anatoly Zak


A view of an open avionics section on the Fregat upper stage. Click to enlarge. Copyright © 2001 Anatoly Zak


S5.92 engine

The S5.92 engine serves as the main propulsion unit of the Fregat upper stage. Click to enlarge. Copyright © 2008 Anatoly Zak


launch

Soyuz-FG rocket launches European Mars Express orbiter on June 2, 2003. Credit: ESA


Flagman upper stage

The Flagman cruise stage of the Phobos-Grunt spacecraft would closely resemble the Fregat orbital tug, minus its flight control system. Apparent changes would include ball-shaped tank extensions, enabling larger propellant loads. Click to enlarge. Copyright © 2009 Anatoly Zak


Fregat

The Fregat-SB variant. Click to enlarge. Credit: NPO Lavochkin


Fregat

A Separable Tank Block (Sbrasyvaemy Blok Bakov) SBB used with the Fregat-SB variant. Click to enlarge. Credit: NPO Lavochkin


fregat-sbu

A Fregat-SBU variant as of 2018. Credit: NPO Lavochkin