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Last Updated: 28 December 2005

PRITHVI SRBM


© Arun Vishwakarma


Introduction

Prithvi is a Sanskrit/Hindi word meaning Earth, given that it is a surface-to-surface missile. The Prithvi is among the most modern short-ranged battlefield missiles in the world. It has the highest warhead-weight to overall-weight of any missile in its class, thanks to its unique aerodynamic design with delta wings located mid-body that allow it to glide during flight.

Development

India launched the Integrated Guided Missile Development Program (IGMDP) in 1983 to concurrently develop & produce a wide range of missiles for surface-to-surface and surface-to-air roles. Prithvi was the first missile developed as part of IGMDP. Agni, Prithvi, Trishul, Akash, Nag and Astra also form part of the IGMDP, which is being managed by the Defence Research and Development Organisation (DRDO).

The Prithvi missile comes in four variants:
• SS-150/Prithvi-I is a battlefield support system for the army (range 150 km, 1000 kg payload). It is a single stage, dual engine, liquid fuel, road-mobile, short-range surface-to-surface missile
• SS-250/Prithvi-II is dedicated to the Indian Air Force (range 250 km, 500 - 750 kg payload). It is a single stage, dual engine, liquid fuel, road-mobile, short-range surface-to-surface missile. DRDO has decided to increase the payload capability of the SS-250/Prithvi-II variant to 1000 kg by using boosted liquid propellant to generate higher thrust-to-weight ratio [1].
• SS-350/Prithvi-III is a solid fuelled version with a 350 km range and a 1000 kg payload. It is a two stage, solid fuel, road-mobile, short-range, surface-to-surface missile. Sagarika and Prithvi-III are two different acronyms for the same missile [2]. A related program, known as Project K-15, is in development and will enable the missile to be launched from a submerged submarine [3].
• 
Dhanush (in Sanskrit/Hindi means Bow) is a system consisting of a stabilization platform (Bow) and the Missile (Arrow). The system can fire either the SS-250 or the SS-350 variants. There may likely be certain customizations in missile configuration to certify it for sea worthiness.

Some of the ground work for Prithvi was done as part of the earlier projects known as Project Devil [4] and Project Valiant [5]. The two Prithvi liquid engines are derived from scaling down the 30-ton Valiant engine and scaling up the Russian V-755 engine used by SA-2 surface-to-air missile, using 'IRFNA' [inhibited red-fuming nitric acid] as an oxidizer and G-fuel (Xylidiene and Tri-ethylamine). Prithvi can also be launched from warships equipped with the Dhanush (Sanskrit/Hindi word for Bow, as in bow & arrow), a hydraulically stabilized launch pad. By October 1995, 20 pre-production Prithvi SS-150s were delivered to the Army to form the 333rd Missile Group based in Secunderabad. Two additional units have been formed since, the 444th Missile Group and 555th Missile Group.

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The various warheads the
Prithvi SRBM can carry

Test flight of the
Prithvi SS-150

A feature comparison between
the SS-250 and SS-350 variants

Typically, each group has 12 launchers, with possibly another three more in reserve. Reportedly 300 Prithvis, estimated to cost $200 million, would be manufactured at the state-owned Bharat Dynamics Limited (BDL) in Hyderabad at the rate of 36 missiles/year. Various technical tests of the SS-250 variant have been carried out, and a recent one on 31 March 2001 reportedly carried multiple payloads over 250 km and was solid-fuelled. On 18 April 2001 in Parliament, then-incumbent Defence Minister Jaswant Singh stated that the SS-250 was being inducted into the IAF, but apparently the IAF plans to use it only for familiarization/training. The Prithvi program has continued to develop newer versions with improved range and accuracy. The tests on 23 January 2004 and 19 March 2004 were of the longer range, solid fuelled Prithvi-III variant meant for the IAF and were reportedly successfully tested for the 'runway denial' mission. Earlier tests in December 2001 proved an advanced homing facility.

Significantly, in December 1998 the Indian Army deployed the Prithvi SS-150 variant in a major military exercise for the first time since its induction. Code-named Exercise Shiv Shakti '98, the military exercise signified that the Prithvi had been further inducted into the military doctrine. If the missile is deployed in states like Kashmir, Punjab and Gujarat which border Pakistan, it would place the cities of Islamabad, Lahore, Karachi, Hyderabad and many of Pakistan's strategic military installations within its range. An unspecified number of Prithvi missiles are based near Jalandhar in northern Punjab, for potential use as a tactical battlefield missile against Pakistan. The unit cost of a Prithvi missile in 2004 is approximately Rs.7 crore (US $1.4 million).

Strategic vs. Conventional Role

Although Prithvi is capable of carrying nuclear/strategic warheads, it is dedicated for battlefield use making use of conventional payloads such as pre-fragmented explosives, bomblets, incendiary, cluster munitions, sub-munitions, fuel-air and high explosives [6]. Prithvi warheads are field interchangeable. The Prithvi was India's sole ballistic missile for many years before induction of the Agni-I/II intermediate range missiles. Thus even though the Prithvi missile groups had conventional warheads, it was assumed within the international strategic community that some were (or could be at short notice) configured with a strategic nuclear payload [7]. This created a problem for the Indian strategic community related to the concern that advanced deployment of the Prithvi during a build-up to war could blur the nuclear threshold and be destabilizing. This issue became a reality in June 1999 at the height of the Kargil imbroglio. The concern was that advanced deployment of the Prithvi could be misinterpreted as lowering the nuclear threshold. Yet press reports after the crisis was resolved, indicated that four Prithvis and one Agni were activated.

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Support vehicles for
the
Prithvi SRBM

Prithvi SS-150
on Republic Day
Distinctly blunt nose of Prithvi-III [8] Large size solid booster
ostensibly of Prithvi-III

Obviously the misinterpretation would not have happened if sufficient Agni missiles were around for the task or these were tasked for other targets. Clearly special weapons are complex systems and have deeper ramifications that have to be understood before weaponizing. From the book "Wings of Fire" (by Dr. APJ Abdul Kalam) it is clear that the Prithvi project was implemented as a morale booster for disheartened scientists in DRDL who had worked on the 'Devil' and 'Valiant' programmes that saw development of the 30 ton liquid fuelled engines. Under Dr. Kalam the engineers evaluated the options to build on liquid fuel expertise built from Devil and Valient program versus solid fuelled motor technology developed by ISRO. To keep the morale of the DRDO engineers it was decided to start the project using liquid propellant engine. And after the first few test flights the liquid fuelled Prithvi developed its own constituency. It reflected a sorry state of affairs when a weapons system implemented as a morale booster, ended up creating heartburn about lowering the nuclear threshold [9].

The situation was later corrected with the addition of the Agni-I and Agni-II missiles to the arsenal. Thus Agni missiles exclusively and distinctly serve the role of strategic missile, while the Prithvi Missile Groups are purely for conventional battlefield use. The fact that DRDO was forced to use available technologies and unable to secure support for engine redesign, to incorporate its own superior liquid fuel or the Indian Space Research Organisation's more advanced solid fuel technology, testifies to the limited support for the Prithvi. After the Agni-I MRBM missile test in January 2002, K. Santhanam - former RAW officer, DRDO technical advisor, nuclear scientist and presently IDSA Director - stated that the Prithvi missile was never meant to carry nuclear warheads under normal circumstances. This indicates that the solid-fuelled Agni has completely taken over the 'nuclear' role from the liquid-fuelled Prithvi.

Description

The Prithvi-I is 8.56 meters long and has a diameter of 1.1 meters, while Prithvi-II is 9 meters long but has the same diameter to the Prithvi-I. The rocket motor is approximately 6 meters long, and the warhead cone is about 2.5 meters long.  Different kinds of warheads can be fitted on to the missile, and can be changed under battlefield conditions. The Prithvi-I and II variants are powered by two liquid propellant rocket engines designed & developed by the DRDO. The regeneratively cooled engines are gimbaled to operate independently, making it possible to steer the missile in all three axes using thrust vector control during flight. The single stage missile uses liquid fuel. The hypergolic liquid fuel employs inhibited red fuming nitric acid as an oxidizer and a 50:50 combination of xylidiene and triethlyamine as fuel.

The missile's volatile liquid fuel must be loaded immediately prior to launch, imposing certain delay before it is ready for launch. Once loaded such missiles can stay in ready state for few months, however they can be loaded/unloaded only limited number of times. Fuel loading and draining is a very sensitive process, missile crews who operate them undergo intense training in three general phases; missile sub-system, handling and maintenance. An advanced simulator has been developed to train the missile crews in it's operation. The fuel tank is made of light aluminium alloy and completely sealed to facilitate easy cross-country transportation. The missile can be rapidly deployed from the vehicle and fired from a single launcher. Liquid fuel also allows greater in-flight maneuvering capability; the missile is capable of being maneuvered up to 15º in flight.

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Prithvi SS-150 on
a Tatra 4x4 truck

Flight profile of the Prithvi SRBM

Prithvi  SS-250, the
Indian Air Force variant

Gimbaled engine nozzle

The Prithvi-III is a solid fuelled missile and its motor diameter is 1.0 meters, with a length of 6 meters. It uses a high energy solid propellant (HTPB/AP/Al)[23] that allows greater range (350 to 600 km) and payload (500 to 1000 kg) capability. The missile has a distinctly new blunt nose cone/RV, characteristic of high-speed re-entry of longer range missiles. Some reports indicate that Prithvi-III is a two stage missile with a RV integrated second stage [10], that is likely to have a range of 1000 km with a 500 kg payload. The missile is unlikely to have four clipped delta wings midsection of the missiles that is typical of Prithvi-I and -II, and will rather have four small fins towards its rear to provide necessary manoeuvring on re-entry using body lift. The case-bonded HTPB-based composite propellant and composite nozzle generate 16 tons of thrust for a duration of 38 seconds [11].

The solid fuelled Prithvi is self-contained, unlike the liquid fuelled Prithvi that require a large number of support vehicles. Also unlike its liquid engine counterpart, solid fuel is stable and does not require human handling. However liquid filled missiles are more accurate because the navigation & control systems can precisely control the impulse from the engine by controlling or limiting its thrust. Solid fuelled rockets cannot turn off thrust on demand and further due to manufacturing variances, actual impulse from a solid motor is not known in advance. These factors make control & aiming more challenging and thus missile accuracy suffers unless mitigated by other means. Prithvi-III retains the high accuracy of its liquid fuelled counterparts, by using aerodynamic control forces available all along its flight in higher and lower reaches of the atmosphere.

The Prithvi has four distinctive large clipped tip delta wings (2.6 meter span) located in the middle of the fuselage that gives significant manoeuvring capability to defeat ABM defenses. Four smaller fins at the rear of the missile are used to control the missile's attitude and augment range using aerodynamic lift from the lifting body. Once fired, the missile is controlled by the gimbaled engine as well as the aerodynamic force from the wings and fins. Prithvi-II missile typically reaches a maximum altitude of approximately 80 km (Mach 4), thus spending most of the flight time in the upper reaches of the atmosphere. The large delta wings and body lift is used to generate additional lift during ascent and descent, allowing it to overcome the range restriction associated with pure ballistic flight. During descent, the large delta-wings in the mid-section generates lift allowing the missile to glide and fly (Mach 5) on a trajectory different from the predictable trajectory of a pure ballistic missile and ends in a steep descent at nearly 80° for superior CEP (see Prithvi trajectory diagram above). Prithvi-I ascends to peak speed of 900m/sec when the thrust is cutoff and it raises to an altitude of 30Km before it glides to the target it. Prithvi-II does not limit the peak velocity and it also has larger fuel load. 

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Prithvi missile  test at sea from a Dhanush stabilizer

The Prithvi missile mounted on a Dhanush Stabilizer in a Sukanya Class patrol vessel, all of which are scale models on display

Prithvi missile  test at sea from a Dhanush stabilizer [8]

The Dhanush Stabilizer Dual redundant Fire Control System Fire Control System Graphical User Interface

The Prithvi can execute up to five waypoints en route to the target, thus maximizing the element of surprise. This makes it difficult for ABM defenses to intercept the missile. The missile is coated with radar-absorbing paint to reduce its radar signature during flight, thus further reducing the probability of detection and interception. The missile's lifting configuration allows a shallower re-entry course, and steering along the way. This permits attacking targets not in line with the missile's launch azimuth and reduces turbulence and re-entry thermal stress. The shallow glide also allows better terminal guidance accuracy. The delta wing is placed at the center-of-mass of expended missile. Since the liquid-fuelled engine is tail heavy as against the solid-fuelled stage, the delta wing on the Prithvi-I/II variants are back-set & located approximately 3.2 meters (from tail) as against the Prithvi-III, where the fins are located a little forward (approximately 3.6 meters from tail).

The Prithvi uses a closed-loop, Strap-down Inertial Navigation System (SINS) for navigation and flight control. The SINS computer uses twin microprocessors and the missiles is guided to the target within a CEP (Circular Error Probable) equal to 0.01% of its range. During test, the missile reportedly achieved high accuracy rate. Unconfirmed reports suggest that some Prithvi missiles might have a radar scene correlation terminal guidance system [12]. India integrated indigenously developed GPS receiver for augmentation of targeting accuracy to a few meters' CEP. India and Russia are working together on the development of a new generation of Global Navigation Satellite System (GLONESS) known as the Global’ Naya Navigatsionnaya Sputnikovaya Sistema that will be operational by 2007 [24]. Glonass-K satellites will be launched by Russian and Indian launchers and India will have access to military grade P code signal. The Prithvi-II reportedly has a terminal homing guidance and anti-radiation systems. A scheme to retrofit the Prithvi-I, with this capability, is planned. This capability is useful in attacking hard targets like armoured concentrations in their parking sites or radars. For field operations, the missile will be transported on an all-terrain, eight wheel Kolos Tatra 4x4 truck. The missile is deployed from the vehicle and fired from a simple launcher. Each battery of four Prithvi carrier vehicles will be accompanied by a missile re-supply & loading vehicle, a propellant tanker (only for the liquid-fuelled Prithvi-I & II variants) and also a command post to provide target data to the missile's guidance system before launch. It also has an integrated surveillance & mission support capability and other support vehicles and equipment. The Prithvi-III/SS-350 can be launched from the surface of the sea, as well as from under the sea [13].

  Prithvi-I
SS-150
Prithvi-II
SS-250
Prithvi-III
SS-350
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Length (m) 9 8.56 8.56
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Maximum Diameter (m) 1.1 1.1 1.0 [14]
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Number of Stages -1 -1 2 (?)
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Launch Weight (Kg)
*Including Payload
4,400 4,600 5,600
- - - -
Propellant Liquid
(IRFNA and Xylidiene
plus Triethylamine)
Liquid
(IRFNA and Xylidiene
plus Triethylamine)
Solid
(HTPB/AP/Al)
- - - -
Number of Engines Two (gimbaled) Two (gimbeled) One
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Case Material Aluminium Alloy Aluminium Alloy Steel
- - - -
Stage Fuel-Mass-Ratio 0.79 [15] 0.79 [16] 0.76 [17]
- - - -
Payload (kg) 800 - 1000 800 - 1000 500 - 1000
- - - -
Guidance

Strapped-INS, optionally augmented by GPS

Terminal guidance: Radar scene correlation?

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Range (km)

150 250 350 - 600
- - - -

Accuracy (CEP)

10 - 50 metres 75 metres 25 metres
- - - -

Control System

Gimbaled engines plus
aerodynamic control surfaces
Aerodynamic control
surfaces
- - - -

Launch platform

8 x 8 Tatra Transporter Erector Launcher

Prithvi - Test Flight Chronology

01] February 25, 1988 - Prithvi-1 at Sriharikota

02] November 1989 - Prithvi-1. (Partially successful) In terminal phase the missile rolled uncontrollably due to Inertial Measurement Unit  defect and missed the target by several kilometer.[20]

03] February 11, 1991 - Prithvi-1

04] July 04, 1991 - Prithvi-1.  Initial launch was aborted due to problem with  engine pyro igniter.[21]

05] August 07, 1991 - Prithvi-1

06] February 13, 1992 - Prithvi-1 (Failure) Missile lost control after launch. Engine gimbal lug failure in response to spurious perturbation in IMU sensors.[22] 

07] May 05, 1992 - Prithvi-1 at ITR Balasore

08] August 18, 1992 Prithvi-1 

09] August 29, 1992 Prithvi-1

10] February 07, 1993 - Prithvi-1 at ITR Balasore (10th Test)

11] June 12, 1993 - Prithvi-1

12] November 30, 1993 - Prithvi-1 at ITR Balasore with 250 kg payload

13] June 04, 1994 - Prithvi-1 at ITR Balasore

14] June 06, 1994 - Prithvi-1 at ITR Balasore

15] January 27, 1996 - Prithvi-2 at ITR Balasore

16] 1996 - Prithvi-2 at ITR Balasore

17] February 23, 1997 - Prithvi-2 at ITR Balasore

18] April 11, 2000 - Dhanush/Prithvi-2 at ITR Chandipur (Failure)

19] June 16, 2000 - Prithvi-2 at ITR Chandipur

20] March 31, 2001 - Prithvi-2 at ITR Chandipur (Solid fuel test)

21] September 21, 2001 - Dhanush/Prithvi-? (Ship launched INS Subhadra)

22] December 12, 2001 - Prithvi-2 at ITR Chandipur (Indian Air Force)

23] March 26, 2003 - Prithvi-2 (16th Trial) Using indigenously developed GPS for greater accuracy.

24] April 29, 2003 - Prithvi-2 at ITR Balasore

25] January 23, 2004 - Prithvi-3 solid fuelled at ITR Balasore (23rd Test)

26] March 19, 2004 - Prithvi-3 solid fuelled at ITR Balasore

27] October 27, 2004 – Prithvi-3 solid fuelled at ITR Chandipur . Underwater launch from an artificially made water base [18]. First mention of Prithvi as Medium Range Missile.

28] November 07, 2004 – Dhanush/Prithvi-2 (Ship launched INS Subhadra) [19]

29] May 12, 2005 - Prithvi-3 at ITR Balasore 

30] Dec 28,2005 -Dhanush, INS Rajput, in sea near Paradeep 


Footnotes

[1] Anupam Srivastav: Strategic Import of Missiles in the Indian Security Policy, 20-22 May 1999, City Hall, Como.

[2] Naval Prithvi testing soon. The Tribune, 07 Sept 1998, (www.tribuneindia.com/1998/98sep07/head6.htm). Quote: Defence Ministry sources said that Sagarika and Prithvi-III (naval Prithvi) were one and the same thing or two sides of the same coin. "These (Sagarika and Prithvi-III) are two different acronyms for the same missile for the Indian Navy which is under development," the sources explained.

[3] DRDO: Launching platforms for Project K-15, (http://www.drdo.com/pub/techfocus/aug04/missile13.htm).
India tests medium-range missile: BBC, 27 October 2004, (http://news.bbc.co.uk/1/hi/world/south_asia/3957587.stm).
Prithvi-III test fired: The Times of India, 27 October 2004, (http://timesofindia.indiatimes.com/articleshow/901642.cms).

[4] Project 'Devil' was the effort to reverse engineer the SA-2 SAM.

[5] Weapons of Peace, Raj Chengappa. Project 'Valiant' was a secret project to develop India’s first multi-stage ICBM.

[6] Mark Tully, 'Indian Nuclear Posture'

[7] The nuclear tests conducted in May 1998 proved that miniaturized nuclear warheads of various yields can also be fitted and Dr. APJ Abdul Kalam, the then-incumbent Scientific Advisor to the Government and DRDO Chief, stated that a few days after the Shakti-98 nuclear tests. However, after the Agni-I MRBM test in January 2002, K. Santhanam - former RAW officer, DRDO technical advisor, nuclear scientist and presently IDSA Director - stated that the Prithvi missile was never meant to carry nuclear warheads under normal circumstances. This indicates that the solid-fuelled Agni has completely taken over the 'nuclear' role from the liquid-fuelled Prithvi.

[8] Stubby nosed Prithvi-III missile photo accidentally released by MoD. Ministry Of Defense Annual Reports 2001- 2002. Chapter-8.
http://mod.nic.in/reports/report02/chap8.pdf

[9] D. Ramana, Agni-I, www.bharat-rakshak.com

[10] Prithvi-III test-fired for first time: The Hindu, 28 October 2004, (http://www.hindu.com/2004/10/28/stories/2004102807641300.htm).

[11] 'Large Size Solid Booster' DRDO Technology Focus Vol. 9 No.5 October 2001 ISSN: 0971 - 4413
http://www.drdo.com/pub/techfocus/oct2001/propulsion.htm

[12] Prithvi (SS-150/-250/-350) (P-1/P-2/P-3) and Dhanush: http://www.aeronautics.ru/archive/wmd/ballistic/

[13] Naval Prithvi testing soon. The Tribune, 07 Sept 1998, (www.tribuneindia.com/1998/98sep07/head6.htm). Quote: It is understood that the naval Prithvi will have the distinction of being capable of launch from both a ship or a submarine.

[14] A DRDO publication (DRDO Technology Focus Vol. 9  No.5  October  2001) suggest the diameter may be as small as 0.75 meters.

[15] Estimated by using BR rocket simulator (ROCKSIM) to work backward the configuration for stated configuration & performance.

[16] Estimated by using BR rocket simulator (ROCKSIM) to work backward the configuration for stated configuration & performance.

[17] Estimated by using BR rocket simulator (ROCKSIM) to work backward the configuration for stated configuration & performance.

[18] Doordarshan (www.ddindia.com) 28 October 2004. "This is for the first time that the missile, which has the capability to be launched underwater, was put to trial from an artificially made water base with the help of a specially designed canister."

[19] Test fire of Dhanush, MoD Press Release, 08 December 2004
.......Dhanush successfully test fired, MoD Press Release, 08 November 2004.

[20] Weapons Of Peace -Raj Changappa. Page-361.

[21] ibid. Page-362.

[22] ibid. Page-362.

[23] 'Large Size Solid Booster' DRDO Technology Focus Vol. 9 No.5 October 2001 ISSN: 0971 - 4413 http://www.drdo.com/pub/techfocus/oct2001/propulsion.htm

[24] Deccan Herald, 20 Dec 2005. "Indo-Russian tie-up on Glonass satellite system". http://www.deccanherald.com/deccanherald/dec202005/state1861820051219.asp

.......DNA India, 04 Dec 2005. "Indian military may match GPS with Russian satellites" http://dnaindia.com/report.asp?NewsID=1000431

.......Mosnews.com, 16 Nov 2005. "India to Use Russian Satellite Navigation System — Minister" http://www.mosnews.com/news/2005/11/16/indiasatellite.shtml 

.......New Scientist.com news service, 02 Dec 2005, "India to help Russia boost satellite navigation system" http://www.newscientistspace.com/article.ns?id=dn8416


Sources, References and Acknowledgement

1. Raj Chengappa, Weapons of Peace: The Secret Story of India's Quest to be a Nuclear Power (New Delhi: Harper Collins Publishers India, 2000, ISBN 81-7223-332-0).

2. Defence Research & Development Organization (www.drdo.com).

3. DRDO periodicals "Technology Focus" bi-weekly (www.drdo.com/pub/techfocus/welcome3.htm).

4. Indian Defence Technology: Missile Systems (DRDO, Ministry of Defence, December 1998).

5. Nuclear Threat Initiative (www.nti.org)

6. Ministry of Defense - Annual Reports: 1999 to 2005 (http://mod.nic.in/reports/)

7. The author gratefully acknowledges DRDO &  Ministry of Defense (Government of India) for use of photographs.


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