Source: Kompas Newspaper
RX-420 rocket with diameter 420 mm and length 6.2 m was the biggest rocket that successfully launched into space by Indonesian LAPAN in last 10 years. With weight 300 kgs, RX-420 flew until 101 kms ground to ground with vertical height 53 kms and speed up to 4.4 machs. This successful launch is a key step to satellite launch vehicle (SLV) that scheduled by LAPAN to be launched in 2014. In that configuration, RX-420 rocket is the main component of LAPAN SLV.
To transport a satellite in orbital position with height 300 kms, the SLV is designed to be consisted of four-stage propulsion, started with RX-420 (3 units) in the bottommost position as booster, two RX-420 rockets in the second stage and third stage and RX-320 rocket as the latest stage at the top position. This design has length 9,496 mm with total weight is 3.8 tons. One RX-420 rocket weighs around 2 tons with cruise distance 120 kms. With the current SLV configuration, the vertical launch distance may reach 300 kms. This SLV will carry 50 kgs load until the orbital position at height 250 kms. Horizontal speed of the rocket is planned to be around 7-8 kms/sec.
Evaluating the last week launching experiment of RX-420 rocket, LAPAN’s chairman Adi Sadewo Salatun said that LAPAN still requires an improvement or correction particularly at fin, nozzle and propellant components. “The homework has to be finished is to enhance octane value or impulse specific (Isp) from 230 to 300,” he said. For that objective, LAPAN will select finer grain size of ammonium perchlorate (AP) as rocket solid fuel. Currently besides using AP, LAPAN uses aluminum, HTPB (Hidroxy Terminated Polybutadiene) and TDI (Toluena Diisocyanate). As comparison, Chinese uses 9 (nine) combination of material for their SLV solid fuel.
An increased thrust power of the rocket by means of improving Isp can be provided by combining the solid fuel ingredients from four to seven types of material (a combination of solid ingredients, oxidators and additives). For propellant requirement, the factory of AP will increase its production from 2 tons/year to be 10 tons/year.
A correction also will be performed at the nozzle part as ports or conduit of gas exhaust. According to Head of RX-420 Engineering, Lilis Maryani, the nozzles component of that rocket will be reduced its weight about 40% less. Presently, its weight is 90 kgs with graphite block material.
A ratio between structure and propellant weight now is still 50:50. It will be modified to more ideal ratio by reducing the structure weight 200 kgs less to boost additional rocket speed 3 kms/sec for higher/longer cruise distance. Presently, manufacturing of nozzles were done by milling technique. “To reduce the weight as an improvement, nozzles will be made by casting method through cooperation with state owned steel manufacturer, Krakatau Steel (KS),” Adi added. Cast nozzles will be made from steel and aluminum alloy. Future static test will be performed in December 2009 and next rocket launch test is scheduled in 2010, that is two-stage RX-420 rocket for motor test. The distance (ground to ground) is expected increases from 100 kms to 150 kms. Referring to that configuration, Head of SLV Engineering, Rika Andiarti, said that next year LAPAN will start developing inter-rocket separation system and nozzles at height 20 kms atmosphere condition while second stage motor is ignited.
Adi said,” Another issue is cracked rocket fins problem from the latest experiment due to major influence of localized aerodynamics heating in velocity 4.4 machs or 1.2 kms/sec”. Lilis added,” It will be corrected by adding heat insulator”.
Four-stage configuration of RX-420 and RX-320 which is adopted so far by LAPAN for their SLV still has a disadvantages especially on strap on booster rockets. “If this configuration is not working, we will choose an alternative configuration of combined RX-520 and RX-420 to reduce the structure weight and to increase the rocket speed”, said Adi.
For the rocket payload, Head of LAPAN Payload Engineering, Herma Yudhi Irwanto, said that for future experiment LAPAN will develop vibration dampener for rocket payload, including satellite. In this issue, satellite test engine has been built using LAPAN A1 and A2 satellite technology. The latest info gathered from LAPAN, they will make mobile vehicle as launching truck for other location alternatives, instead of current Pameungpek location, such as in Ujung Kulon-West Java Province and Southern Beach of Bengkulu Province (Sumatera Island). For this year, LAPAN gets additional budget from Rp 30B (US$ 3M) to Rp 50B (US$ 5M) for RX-420 development and RX-520 research.