Error log

Thanks for using Andrew's Aerospace Calculator Version 2.0
For the following inputs, either give a number or put 'unknown'
Also, please round decimals to the nearest hundredth or add zeros so that you have hundredths.
What is the height in meters?
"1000.00"
What is the temperature in degrees celsius?
"unknown"
What is the pressure in kPa?
"unknown"
What is the density in kg/m^3?
"unknown"
What would you like to find? (Enter a number)
1) Temperature
2) Pressure
3) Density
"1"
Calculating Temperature...
Exception in thread "main" java.lang.NumberFormatException: For input string: "unknown"
	at sun.misc.FloatingDecimal.readJavaFormatString(Unknown Source)
	at java.lang.Double.parseDouble(Unknown Source)
	at calculator.AerospaceCalculator.findTemp(AerospaceCalculator.java:73)
	at calculator.AerospaceCalculator.main(AerospaceCalculator.java:44)