CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (20,675)	$ (14,408)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization expense	418	362
Stock-based compensation	2,252	2,144
Gain on PPP Loan forgiveness	(662)	0
Other	39	148
Change in operating assets and liabilities:
Contracts and other receivables	503	(2,859)
Prepaid materials	304	536
Prepaid expenses and other assets	784	145
Accounts payable	51	(219)
Accrued liabilities	193	(208)
Accrued research and development expenses	1,250	380
Accrued compensation	(316)	(416)
Operating lease right-of-use assets and liabilities, net	291	(112)
Contract liabilities	0	(6)
Other liabilities	(729)	(1,212)
Net cash used in operating activities	(16,297)	(15,725)
Investing activities
Purchases of property and equipment	(210)	0
Acquisition of intangibles	0	(11)
Net cash used in investing activities	(210)	(11)
Financing activities
Proceeds from borrowing under Paycheck Protection Program	0	662
Proceeds from issuance of common stock, net	21,384	3
Proceeds from exercise of common stock options	27	0
Principal payments on term loan	0	(1,000)
Payments on financing leases	(81)	(207)
Net cash provided by (used in) financing activities	21,330	(542)
Net increase (decrease) in cash and cash equivalents	4,823	(16,278)
Cash and cash equivalents at beginning of period	31,087	34,121
Cash and cash equivalents at end of period	35,910	17,843
Reconciliation of cash, cash equivalents and restricted cash
Cash and cash equivalents	35,848	17,843
Restricted cash	62	0
Total cash, cash equivalents and restricted cash	35,910	17,843
Supplemental disclosure of cash flow information
Paycheck Protection Program loan forgiveness	662	0
Interest paid	(329)	(1,066)
Income taxes paid	$ (1)	$ (1)